{"id":51367,"date":"2020-01-26T13:47:46","date_gmt":"2020-01-26T12:47:46","guid":{"rendered":"https:\/\/www.thermal-engineering.org\/o-que-e-o-ciclo-otto-otto-engine-definicao\/"},"modified":"2021-06-04T14:13:47","modified_gmt":"2021-06-04T13:13:47","slug":"o-que-e-o-ciclo-otto-otto-engine-definicao","status":"publish","type":"post","link":"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-o-ciclo-otto-otto-engine-definicao\/","title":{"rendered":"O que \u00e9 o Ciclo de Otto &#8211; Motor de Otto &#8211; Defini\u00e7\u00e3o"},"content":{"rendered":"<div class=\"su-quote su-quote-style-default\">\n<div class=\"su-quote-inner su-clearfix\">O ciclo do mecanismo Otto \u00e9 chamado de ciclo Otto. \u00c9 um dos ciclos termodin\u00e2micos mais comuns que podem ser encontrados em motores de autom\u00f3veis. Ciclo de Otto &#8211; Motor de Otto<\/div>\n<\/div>\n<div class=\"su-divider su-divider-style-dotted\"><\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-50 lgc-tablet-grid-50 lgc-mobile-grid-100 lgc-equal-heights lgc-first\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<h2>\u00a0Ciclo de Otto &#8211; Motor de Otto<\/h2>\n<p>Em 1876, um engenheiro alem\u00e3o,\u00a0<strong>Nikolaus August Otto,<\/strong>\u00a0avan\u00e7ou no estudo de motores t\u00e9rmicos construindo o primeiro motor de quatro tempos em funcionamento.\u00a0um motor estacion\u00e1rio usando uma mistura de carv\u00e3o-g\u00e1s-ar como combust\u00edvel.\u00a0Wilhelm Maybach (1846-1929), um dos mais importantes engenheiros alem\u00e3es, aperfei\u00e7oou a constru\u00e7\u00e3o, que foi produzida em grandes quantidades j\u00e1 no final do ano de 1876. Essas inven\u00e7\u00f5es rapidamente remodelaram o mundo em que viviam.<\/p>\n<p>O ciclo do mecanismo Otto \u00e9 chamado de ciclo Otto.\u00a0\u00c9 um dos\u00a0<strong>ciclos termodin\u00e2micos<\/strong>\u00a0mais comuns\u00a0encontrados em\u00a0<strong>motores de autom\u00f3veis e<\/strong>\u00a0descreve o funcionamento de um motor de pist\u00e3o de igni\u00e7\u00e3o comandada t\u00edpico.\u00a0Ao contr\u00e1rio do ciclo de Carnot, o ciclo Otto n\u00e3o executa processos isot\u00e9rmicos, porque estes devem ser realizados muito lentamente.\u00a0Em um ciclo Otto ideal, o sistema que executa o ciclo passa por uma s\u00e9rie de quatro processos revers\u00edveis internamente: dois processos isentr\u00f3picos (adiab\u00e1ticos revers\u00edveis) alternados com dois processos isoc\u00f3ricos.<\/p>\n<p>Como\u00a0<strong>o princ\u00edpio de Carnot<\/strong>\u00a0afirma que nenhum motor pode ser mais eficiente que um motor revers\u00edvel (\u00a0<strong>um motor t\u00e9rmico Carnot<\/strong>\u00a0) operando entre os mesmos reservat\u00f3rios de alta temperatura e baixa temperatura, o motor Otto deve ter uma efici\u00eancia mais baixa que a efici\u00eancia de Carnot.\u00a0Um\u00a0<strong>motor automotivo a gasolina<\/strong>\u00a0t\u00edpico\u00a0opera com cerca de\u00a0<strong>25% a 30%<\/strong>\u00a0de efici\u00eancia t\u00e9rmica.\u00a0Cerca de 70-75% \u00e9 rejeitado como calor residual sem ser convertido em trabalho \u00fatil, ou seja, trabalho entregue \u00e0s rodas.<\/p>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-50 lgc-tablet-grid-50 lgc-mobile-grid-100 lgc-equal-heights lgc-last\">\n<div class=\"inside-grid-column\">\n<figure id=\"attachment_17548\" class=\"wp-caption aligncenter\" aria-describedby=\"caption-attachment-17548\"><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Four-Stroke-Engine-Otto-Engine.gif\"><img loading=\"lazy\" class=\"size-full wp-image-17548 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Four-Stroke-Engine-Otto-Engine.gif\" alt=\"Motor a quatro tempos - motor Otto\" width=\"225\" height=\"300\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Four-Stroke-Engine-Otto-Engine.gif\" \/><\/a><figcaption id=\"caption-attachment-17548\" class=\"wp-caption-text\">Motor a quatro tempos &#8211; motor Otto<br \/>\nFonte: wikipedia.org, trabalho pr\u00f3prio da Zephyris, CC BY-SA 3.0<\/figcaption><\/figure>\n<div class=\"su-youtube su-responsive-media-yes\"><iframe class=\"lazy-loaded\" src=\"https:\/\/www.youtube.com\/embed\/xflY5uS-nnw?\" width=\"340\" height=\"200\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\" data-lazy-type=\"iframe\" data-src=\"https:\/\/www.youtube.com\/embed\/xflY5uS-nnw?\" data-mce-fragment=\"1\"><\/iframe><\/div>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<h2>Ciclo Otto &#8211; Processos<\/h2>\n<figure id=\"attachment_17461\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-17461\"><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Otto-Cycle-PV-Diagram.png\"><img loading=\"lazy\" class=\"size-medium wp-image-17461 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Otto-Cycle-PV-Diagram-300x245.png\" alt=\"Otto Cycle - Diagrama PV\" width=\"300\" height=\"245\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Otto-Cycle-PV-Diagram-300x245.png\" \/><\/a><figcaption id=\"caption-attachment-17461\" class=\"wp-caption-text\">diagrama pV do ciclo Otto.\u00a0A \u00e1rea delimitada pelo caminho completo do ciclo representa o trabalho total que pode ser realizado durante um ciclo.<\/figcaption><\/figure>\n<p>Em um ciclo Otto ideal, o sistema que executa o ciclo passa por uma s\u00e9rie de quatro processos revers\u00edveis internamente: dois processos isentr\u00f3picos (adiab\u00e1ticos revers\u00edveis) alternados com dois processos isoc\u00f3ricos:<\/p>\n<ol>\n<li><strong>Compress\u00e3o isentr\u00f3pica<\/strong>\u00a0(curso de compress\u00e3o) &#8211; O g\u00e1s (mistura combust\u00edvel-ar) \u00e9 comprimido adiabaticamente do estado 1 ao estado 2, conforme o pist\u00e3o se move do ponto morto inferior para o ponto morto superior.\u00a0O ambiente trabalha com o g\u00e1s, aumentando sua energia interna (temperatura) e comprimindo-o.\u00a0Por outro lado, a entropia permanece inalterada.\u00a0As mudan\u00e7as nos volumes e sua taxa (\u00a0<em>V\u00a0<\/em><em><sub>1<\/sub><\/em><em>\u00a0\/ V\u00a0<\/em><em><sub>2<\/sub><\/em>\u00a0) s\u00e3o conhecidas como taxa de compress\u00e3o.<\/li>\n<li><strong>Compress\u00e3o isoc\u00f3rica<\/strong>\u00a0(fase de igni\u00e7\u00e3o) &#8211; Nesta fase (entre o estado 2 e o estado 3), h\u00e1 um volume constante (o pist\u00e3o est\u00e1 em repouso) transferido para o ar a partir de uma fonte externa, enquanto o pist\u00e3o est\u00e1 em repouso no ponto morto superior .\u00a0Esse processo visa representar a igni\u00e7\u00e3o da mistura combust\u00edvel-ar injetada na c\u00e2mara e a subsequente queima r\u00e1pida.\u00a0A press\u00e3o aumenta e a raz\u00e3o (\u00a0<em>P\u00a0<\/em><em><sub>3<\/sub><\/em><em>\u00a0\/ P\u00a0<\/em><em><sub>2<\/sub><\/em>\u00a0) \u00e9 conhecida como \u201ctaxa de explos\u00e3o\u201d.<\/li>\n<li><strong>Expans\u00e3o isentr\u00f3pica<\/strong>\u00a0(golpe de energia) &#8211; O g\u00e1s se expande adiabaticamente do estado 3 para o estado 4, conforme o pist\u00e3o se move do ponto morto superior para o ponto morto inferior.\u00a0O g\u00e1s trabalha nos arredores (pist\u00e3o) e perde uma quantidade de energia interna igual ao trabalho que sai do sistema.\u00a0Novamente a entropia permanece inalterada.\u00a0A raz\u00e3o de volume (\u00a0<em>V\u00a0<\/em><em><sub>4<\/sub><\/em><em>\u00a0\/ V\u00a0<\/em><em><sub>3<\/sub><\/em>\u00a0) \u00e9 conhecida como a raz\u00e3o de expans\u00e3o isentr\u00f3pica, mas para o ciclo Otto, \u00e9 igual \u00e0 taxa de compress\u00e3o.<\/li>\n<li><strong>Descompress\u00e3o isoc\u00f3rica (curso de exaust\u00e3o)<\/strong>\u00a0&#8211; Nesta fase, o ciclo \u00e9 conclu\u00eddo por um processo de volume constante no qual o calor \u00e9 rejeitado do ar enquanto o pist\u00e3o est\u00e1 no ponto morto inferior.\u00a0A press\u00e3o do g\u00e1s de trabalho cai instantaneamente do ponto 4 para o ponto 1. A v\u00e1lvula de escape se abre no ponto 4. O curso de escape ocorre imediatamente ap\u00f3s esta descompress\u00e3o.\u00a0\u00c0 medida que o pist\u00e3o se move do ponto morto inferior (ponto 1) para o ponto morto superior (ponto 0) com a v\u00e1lvula de escape aberta, a mistura gasosa \u00e9 ventilada para a atmosfera e o processo recome\u00e7a.<\/li>\n<\/ol>\n<p>Durante o ciclo Otto, o trabalho \u00e9 realizado no g\u00e1s pelo pist\u00e3o entre os estados 1 e 2 (\u00a0<strong>compress\u00e3o isentr\u00f3pica<\/strong>\u00a0).\u00a0O trabalho \u00e9 realizado pelo g\u00e1s no pist\u00e3o entre os est\u00e1gios 3 e 4 (\u00a0<strong>expans\u00e3o isentr\u00f3pica<\/strong>\u00a0).\u00a0A diferen\u00e7a entre o trabalho realizado pelo g\u00e1s e o trabalho realizado com o g\u00e1s \u00e9 o trabalho l\u00edquido produzido pelo ciclo e corresponde \u00e0 \u00e1rea delimitada pela curva do ciclo.\u00a0O trabalho produzido pelos tempos de ciclo, a taxa do ciclo (ciclos por segundo) \u00e9 igual \u00e0 pot\u00eancia produzida pelo motor Otto.<\/p>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-50 lgc-tablet-grid-50 lgc-mobile-grid-100 lgc-equal-heights lgc-first\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<h2>Processo isentr\u00f3pico<\/h2>\n<p>Um\u00a0<a title=\"Processo isentr\u00f3pico\" href=\"https:\/\/www.thermal-engineering.org\/what-is-isentropic-process-definition\/\"><strong>processo isentr\u00f3pico<\/strong><\/a>\u00a0\u00e9 um\u00a0<a title=\"Processos termodin\u00e2micos\" href=\"https:\/\/www.thermal-engineering.org\/what-is-thermodynamic-process-definition\/\"><strong>processo termodin\u00e2mico<\/strong><\/a>\u00a0, no qual a\u00a0<a title=\"O que \u00e9 entropia\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/what-is-energy-physics\/what-is-entropy\/\"><strong>entropia<\/strong>\u00a0<\/a>do fluido ou g\u00e1s permanece constante.\u00a0Isso significa que o\u00a0<strong>processo isentr\u00f3pico<\/strong>\u00a0\u00e9 um caso especial de um\u00a0<strong>processo adiab\u00e1tico<\/strong>\u00a0no qual n\u00e3o h\u00e1 transfer\u00eancia de calor ou mat\u00e9ria.\u00a0\u00c9 um\u00a0<strong>processo adiab\u00e1tico revers\u00edvel<\/strong>\u00a0.\u00a0A suposi\u00e7\u00e3o de que n\u00e3o h\u00e1 transfer\u00eancia de calor \u00e9 muito importante, pois podemos usar a aproxima\u00e7\u00e3o adiab\u00e1tica apenas em\u00a0<strong>processos muito r\u00e1pidos<\/strong>\u00a0.<\/p>\n<p><strong>Processo isentr\u00f3pico e a primeira lei<\/strong><\/p>\n<p>Para um sistema fechado, podemos escrever a\u00a0<strong><a title=\"Primeira lei em termos de entalpia dH = dQ + Vdp\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/laws-of-thermodynamics\/first-law-of-thermodynamics\/first-law-in-terms-of-enthalpy-dh-dq-vdp\/\">primeira lei da termodin\u00e2mica em termos de entalpia<\/a><\/strong>\u00a0:<\/p>\n<p><strong>dH = dQ + Vdp<\/strong><\/p>\n<p><strong>ou<\/strong><\/p>\n<p><strong>dH = TdS + Vdp<\/strong><\/p>\n<p><strong>Processo isentr\u00f3pico (dQ = 0):<\/strong><\/p>\n<p><strong>dH = Vdp \u2192 W = H\u00a0<\/strong><strong><sub>2<\/sub><\/strong><strong>\u00a0&#8211; H\u00a0<\/strong><strong><sub>1<\/sub><\/strong><strong>\u00a0\u00a0\u00a0\u00a0\u00a0\u2192 H\u00a0<\/strong><strong><sub>2<\/sub><\/strong><strong>\u00a0&#8211; H\u00a0<\/strong><strong><sub>1<\/sub><\/strong><strong>\u00a0=\u00a0<em>C\u00a0<\/em><\/strong><strong><em><sub>P<\/sub><\/em><\/strong><strong><em>\u00a0(T\u00a0<\/em><\/strong><strong><em><sub>2<\/sub><\/em><\/strong><strong><em>\u00a0&#8211; T\u00a0<\/em><\/strong><strong><em><sub>1<\/sub><\/em><\/strong><strong><em>\u00a0) \u00a0\u00a0\u00a0<\/em><\/strong><em>\u00a0(para\u00a0<a title=\"O que \u00e9 o g\u00e1s ideal\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/ideal-gas-law\/what-is-ideal-gas\/\">g\u00e1s ideal<\/a>\u00a0)<\/em><\/p>\n<p><strong>Processo isentr\u00f3pico do g\u00e1s ideal<\/strong><\/p>\n<p>O\u00a0<strong>processo isentr\u00f3pico<\/strong>\u00a0(um caso especial de processo adiab\u00e1tico) pode ser expresso com a\u00a0<a title=\"Lei do g\u00e1s ideal\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/ideal-gas-law\/\"><strong>lei dos gases ideais<\/strong><\/a>\u00a0como:<\/p>\n<p><strong><em>pV\u00a0<sup>\u03ba<\/sup>\u00a0= constante<\/em><\/strong><\/p>\n<p>ou<\/p>\n<p><em><strong>p\u00a0<sub>1<\/sub>\u00a0V\u00a0<sub>1\u00a0<\/sub><sup>k<\/sup>\u00a0= p\u00a0<sub>2<\/sub>\u00a0V\u00a0<sub>2\u00a0<\/sub><sup>k<\/sup><\/strong><\/em><\/p>\n<p>em que\u00a0<strong>\u03ba = c\u00a0<sub>p<\/sub>\u00a0\/ c\u00a0<sub>v<\/sub><\/strong>\u00a0\u00e9 a propor\u00e7\u00e3o de\u00a0<a title=\"Capacidade t\u00e9rmica - Capacidade t\u00e9rmica espec\u00edfica\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/laws-of-thermodynamics\/first-law-of-thermodynamics\/heat-capacity\/\"><strong>aquecimentos espec\u00edficos<\/strong><\/a>\u00a0(ou\u00a0<strong>capacidades de calor<\/strong>\u00a0) para o g\u00e1s.\u00a0Um para\u00a0<strong>press\u00e3o constante (c\u00a0<\/strong><strong><sub>p<\/sub><\/strong><strong>\u00a0)<\/strong>\u00a0e outro para\u00a0<strong>volume constante (c\u00a0<\/strong><strong><sub>v<\/sub><\/strong><strong>\u00a0)<\/strong>\u00a0.\u00a0Observe que essa raz\u00e3o\u00a0<strong>\u03ba\u00a0\u00a0<\/strong><strong>= c\u00a0<\/strong><strong><sub>p<\/sub><\/strong><strong>\u00a0\/ c\u00a0<\/strong><strong><sub>v<\/sub><\/strong>\u00a0\u00e9 um fator na determina\u00e7\u00e3o da velocidade do som em um g\u00e1s e em outros processos adiab\u00e1ticos.<\/p>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-50 lgc-tablet-grid-50 lgc-mobile-grid-100 lgc-equal-heights lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<h2>Processo Isoc\u00f3rico<\/h2>\n<p>Um\u00a0<a title=\"Processo Isoc\u00f3rico - Processo Isom\u00e9trico\" href=\"https:\/\/www.thermal-engineering.org\/what-is-isochoric-process-isometric-process-definition\/\"><strong>processo isoc\u00f3rico<\/strong><\/a>\u00a0\u00e9 um processo termodin\u00e2mico, no qual o\u00a0<strong>volume<\/strong>\u00a0do sistema fechado\u00a0<strong>permanece constante<\/strong>\u00a0(V = const).\u00a0Ele descreve o comportamento do g\u00e1s dentro do recipiente, que n\u00e3o pode ser deformado.\u00a0Como o volume permanece constante, a transfer\u00eancia de calor para dentro ou para fora do sistema n\u00e3o\u00a0<a title=\"Trabalho p\u0394V - Trabalho de Fronteira e Trabalho V\u0394p\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/laws-of-thermodynamics\/first-law-of-thermodynamics\/p%ce%b4v-work-boundary-work-and-v%ce%b4p-work\/\">funciona<\/a>\u00a0, mas altera apenas a\u00a0<a href=\"https:\/\/www.thermal-engineering.org\/what-is-internal-energy-thermal-energy-definition\/\"><strong>energia interna<\/strong><\/a>\u00a0(a temperatura) do sistema.<\/p>\n<p><strong>Processo isoc\u00f3rico e a primeira lei<\/strong><\/p>\n<p>A forma cl\u00e1ssica da\u00a0<a title=\"Primeira Lei da Termodin\u00e2mica\" href=\"https:\/\/www.thermal-engineering.org\/what-is-first-law-of-thermodynamics-definition\/\">primeira lei da termodin\u00e2mica<\/a>\u00a0\u00e9 a seguinte equa\u00e7\u00e3o:<\/p>\n<p><strong>dU = dQ &#8211; dW<\/strong><\/p>\n<p>Nesta equa\u00e7\u00e3o, dW \u00e9 igual a\u00a0<strong>dW = pdV<\/strong>\u00a0e \u00e9 conhecido como\u00a0<a title=\"Trabalho p\u0394V - Trabalho de Fronteira e Trabalho V\u0394p\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/laws-of-thermodynamics\/first-law-of-thermodynamics\/p%ce%b4v-work-boundary-work-and-v%ce%b4p-work\/\">trabalho de fronteira<\/a>\u00a0.\u00a0Ent\u00e3o:<\/p>\n<p><strong>dU = dQ &#8211; pdV<\/strong><\/p>\n<p>No\u00a0<strong>processo isoc\u00f3rico<\/strong>\u00a0e no\u00a0<strong>g\u00e1s ideal<\/strong>\u00a0, todo o calor adicionado ao sistema ser\u00e1 usado para aumentar a energia interna.<\/p>\n<p><strong>Processo isoc\u00f3rico (pdV = 0):<\/strong><\/p>\n<p><strong>dU = dQ \u00a0\u00a0\u00a0\u00a0<\/strong><em>(para g\u00e1s ideal)<\/em><\/p>\n<p><strong>dU = 0 = Q &#8211; W \u2192 W = Q \u00a0\u00a0<em>\u00a0\u00a0\u00a0\u00a0<\/em><\/strong><em>(para g\u00e1s ideal)<\/em><\/p>\n<p><strong>Processo isoc\u00f3rico do g\u00e1s ideal<\/strong><\/p>\n<p>O\u00a0<strong>processo isoc\u00f3rico<\/strong>\u00a0pode ser expresso com a\u00a0<a title=\"Lei do g\u00e1s ideal\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/ideal-gas-law\/\"><strong>lei dos gases ideais<\/strong><\/a>\u00a0como:<\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/isochoric-process-equation-1.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-17465 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/isochoric-process-equation-1.png\" alt=\"processo isoc\u00f3rico - equa\u00e7\u00e3o 1\" width=\"138\" height=\"52\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/isochoric-process-equation-1.png\" \/><\/a><\/p>\n<p>ou<\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/isochoric-process-equation-2.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-17466 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/isochoric-process-equation-2.png\" alt=\"processo isoc\u00f3rico - equa\u00e7\u00e3o 2\" width=\"86\" height=\"66\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/isochoric-process-equation-2.png\" \/><\/a><\/p>\n<p>Em um\u00a0<strong>diagrama pV<\/strong>\u00a0, o processo ocorre ao longo de uma linha horizontal que possui a equa\u00e7\u00e3o V = constante.<\/p>\n<p>Veja tamb\u00e9m:\u00a0\u00a0<a title=\"Lei de Guy-Lussac\" href=\"https:\/\/www.thermal-engineering.org\/what-is-guy-lussacs-law-definition\/\">Lei de Guy-Lussac<\/a><\/p>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-50 lgc-tablet-grid-50 lgc-mobile-grid-100 lgc-equal-heights lgc-first\">\n<div class=\"inside-grid-column\">\n<figure id=\"attachment_17280\" class=\"wp-caption aligncenter\" aria-describedby=\"caption-attachment-17280\"><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Isentropic-Process-characteristics.png\"><img loading=\"lazy\" class=\"size-full wp-image-17280 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Isentropic-Process-characteristics.png\" alt=\"Processo isentr\u00f3pico - caracter\u00edsticas\" width=\"386\" height=\"609\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Isentropic-Process-characteristics.png\" \/><\/a><figcaption id=\"caption-attachment-17280\" class=\"wp-caption-text\">Processo isentr\u00f3pico &#8211; principais caracter\u00edsticas<\/figcaption><\/figure>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-50 lgc-tablet-grid-50 lgc-mobile-grid-100 lgc-equal-heights lgc-last\">\n<div class=\"inside-grid-column\">\n<figure id=\"attachment_17463\" class=\"wp-caption aligncenter\" aria-describedby=\"caption-attachment-17463\"><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Isochoric-process-main-characteristics.png\"><img loading=\"lazy\" class=\"size-full wp-image-17463 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Isochoric-process-main-characteristics.png\" alt=\"Processo isoc\u00f3rico - principais caracter\u00edsticas\" width=\"382\" height=\"468\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Isochoric-process-main-characteristics.png\" \/><\/a><figcaption id=\"caption-attachment-17463\" class=\"wp-caption-text\">Processo isoc\u00f3rico &#8211; principais caracter\u00edsticas<\/figcaption><\/figure>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<h2>Ciclo Otto &#8211; diagrama pV, Ts<\/h2>\n<figure id=\"attachment_17461\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-17461\"><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Otto-Cycle-PV-Diagram.png\"><img loading=\"lazy\" class=\"size-medium wp-image-17461 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Otto-Cycle-PV-Diagram-300x245.png\" alt=\"Otto Cycle - Diagrama PV\" width=\"300\" height=\"245\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Otto-Cycle-PV-Diagram-300x245.png\" \/><\/a><figcaption id=\"caption-attachment-17461\" class=\"wp-caption-text\">diagrama pV do ciclo Otto.\u00a0A \u00e1rea delimitada pelo caminho completo do ciclo representa o trabalho total que pode ser realizado durante um ciclo.<\/figcaption><\/figure>\n<p>O\u00a0<strong>ciclo Otto<\/strong>\u00a0\u00e9 frequentemente plotado em um diagrama press\u00e3o-volume (\u00a0<strong>diagrama pV<\/strong>\u00a0) e em um diagrama temperatura-entropia (diagrama Ts).\u00a0Quando plotados em um diagrama de volume de press\u00e3o, os\u00a0<strong>processos isoc\u00f3ricos<\/strong>\u00a0seguem as linhas isoc\u00f3ricas do g\u00e1s (as linhas verticais), os\u00a0<strong>processos adiab\u00e1ticos se<\/strong>\u00a0movem entre essas linhas verticais e a \u00e1rea delimitada pelo caminho completo do ciclo representa o trabalho total que pode ser feito durante uma opera\u00e7\u00e3o. ciclo.<\/p>\n<p>O diagrama de temperatura-entropia (diagrama\u00a0<strong>Ts<\/strong>\u00a0) no qual o estado termodin\u00e2mico \u00e9 especificado por um ponto em um gr\u00e1fico com\u00a0<a title=\"Entropia espec\u00edfica\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/what-is-energy-physics\/what-is-entropy\/specific-entropy\/\">entropia<\/a>\u00a0(s)\u00a0<a title=\"Entropia espec\u00edfica\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/what-is-energy-physics\/what-is-entropy\/specific-entropy\/\">espec\u00edfica<\/a>\u00a0(s) como eixo horizontal e temperatura absoluta (T) como eixo vertical.\u00a0Os diagramas Ts s\u00e3o uma ferramenta \u00fatil e comum, principalmente porque ajuda a visualizar a transfer\u00eancia de calor durante um processo.\u00a0Para processos revers\u00edveis (ideais), a \u00e1rea sob a curva Ts de um processo \u00e9 o calor transferido para o sistema durante esse processo.<\/p>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<h2>Ciclo Otto &#8211; Motor a Quatro Tempos<\/h2>\n<p>O ciclo Otto \u00e9 um conjunto de processos usados \u200b\u200bpelos motores de combust\u00e3o interna de igni\u00e7\u00e3o por fa\u00edsca (dois tempos ou quatro tempos).\u00a0Nikolaus August Otto primeiro projetou o que \u00e9 conhecido como o motor de quatro tempos.\u00a0Um curso refere-se ao curso completo do pist\u00e3o ao longo do cilindro, em qualquer dire\u00e7\u00e3o.\u00a0Portanto, cada um deles n\u00e3o corresponde ao processo termodin\u00e2mico \u00fanico fornecido no cap\u00edtulo\u00a0<strong>Ciclo Otto &#8211; Processos.<\/strong><\/p>\n<p><strong>O motor de quatro tempos compreende:<\/strong><\/p>\n<ul>\n<li><strong>o curso de admiss\u00e3o &#8211;<\/strong>\u00a0O pist\u00e3o se move do ponto morto superior (TDC) para o ponto morto inferior (BDC) e o ciclo passa pelos pontos\u00a0<strong>0 \u2192 1.<\/strong>\u00a0Nesse curso, a v\u00e1lvula de admiss\u00e3o \u00e9 aberta enquanto o pist\u00e3o puxa uma mistura de ar e combust\u00edvel para dentro do cilindro produzindo press\u00e3o de v\u00e1cuo no cilindro atrav\u00e9s de seu movimento descendente.<\/li>\n<li><strong>o curso de compress\u00e3o &#8211;<\/strong>\u00a0O pist\u00e3o se move do ponto morto inferior (BDC) para o ponto morto superior (TDC) e o ciclo passa pelos pontos\u00a0<strong>1 \u2192 2.\u00a0<\/strong>Nesse curso, as v\u00e1lvulas de admiss\u00e3o e de escape est\u00e3o fechadas; portanto, a mistura combust\u00edvel-ar \u00e9 comprimida.\u00a0No final deste curso, a mistura combust\u00edvel-ar \u00e9 inflamada por uma fa\u00edsca, o que causa um aumento adicional na press\u00e3o e temperatura na c\u00e2mara.\u00a0No final deste curso, a cambota completou uma revolu\u00e7\u00e3o completa de 360 \u200b\u200bgraus.<\/li>\n<li><strong>o curso de for\u00e7a &#8211;<\/strong>\u00a0O pist\u00e3o se move do ponto morto superior (TDC) para o ponto morto inferior (BDC) e o ciclo passa pelos pontos\u00a0<strong>2 \u2192 3 \u2192 4.<\/strong>\u00a0Nesse curso, as v\u00e1lvulas de admiss\u00e3o e de escape est\u00e3o fechadas.\u00a0No in\u00edcio do curso de for\u00e7a, uma fa\u00edsca inflama a mistura combust\u00edvel-ar na c\u00e2mara de combust\u00e3o, que por sua vez causa uma combust\u00e3o muito r\u00e1pida do combust\u00edvel.\u00a0Nesse golpe, o pist\u00e3o \u00e9 direcionado para o eixo de manivela, o volume aumenta e a press\u00e3o cai \u00e0 medida que o trabalho \u00e9 feito pelo g\u00e1s no pist\u00e3o.<\/li>\n<li><strong>o curso de escape.\u00a0<\/strong>O pist\u00e3o se move do ponto morto inferior (BDC) para o ponto morto superior (TDC) e o ciclo passa pelos pontos\u00a0<strong>4 \u2192 1 \u2192 0.<\/strong>\u00a0Nesse curso, a v\u00e1lvula de escape est\u00e1 aberta enquanto o pist\u00e3o puxa os gases de escape para fora da c\u00e2mara.\u00a0No final deste curso, a cambota completou uma segunda revolu\u00e7\u00e3o completa de 360 \u200b\u200bgraus.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<h2>Compara\u00e7\u00e3o dos ciclos Otto reais e ideais<\/h2>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Otto-engine-vs.-Otto-cycle.png\"><img loading=\"lazy\" class=\"alignright wp-image-17556 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Otto-engine-vs.-Otto-cycle.png\" alt=\"Motor Otto vs. ciclo Otto\" width=\"332\" height=\"556\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Otto-engine-vs.-Otto-cycle.png\" \/><\/a>Nesta se\u00e7\u00e3o, \u00e9 mostrado um\u00a0<strong>ciclo Otto ideal,<\/strong>\u00a0no qual existem muitas\u00a0<strong>suposi\u00e7\u00f5es<\/strong>\u00a0diferentes do\u00a0<strong>ciclo Otto real<\/strong>\u00a0.\u00a0As principais diferen\u00e7as entre o mecanismo Otto real e ideal aparecem na figura.\u00a0Na realidade, o ciclo ideal n\u00e3o ocorre e h\u00e1 muitas perdas associadas a cada processo.\u00a0Para um ciclo real, a forma do diagrama de pV \u00e9 semelhante ao ideal, mas a \u00e1rea (trabalho) delimitada pelo diagrama de pV \u00e9 sempre menor que o valor ideal.\u00a0O ciclo Otto ideal \u00e9 baseado nas seguintes premissas:<\/p>\n<ul>\n<li><strong>Ciclo fechado.\u00a0<\/strong>\u00a0A maior diferen\u00e7a entre os dois diagramas \u00e9 a simplifica\u00e7\u00e3o dos movimentos de admiss\u00e3o e escape no ciclo ideal.\u00a0No curso de escape, o calor Q\u00a0<sub>out<\/sub>\u00a0\u00e9 ejetado para o ambiente, em um motor real, o g\u00e1s sai do motor e \u00e9 substitu\u00eddo por uma nova mistura de ar e combust\u00edvel.<\/li>\n<li><strong>Adi\u00e7\u00e3o instant\u00e2nea de calor<\/strong>\u00a0(\u00a0<strong>adi\u00e7\u00e3o<\/strong>\u00a0isoc\u00f3rica de calor).\u00a0Em motores reais, a adi\u00e7\u00e3o de calor n\u00e3o \u00e9 instant\u00e2nea; portanto, o pico de press\u00e3o n\u00e3o est\u00e1 no TDC, mas logo ap\u00f3s o TDC.<\/li>\n<li><strong>Sem transfer\u00eancia de calor (adiab\u00e1tico)<\/strong>\n<ul>\n<li>Compress\u00e3o &#8211; O g\u00e1s (mistura combust\u00edvel-ar) \u00e9 comprimido adiabaticamente do estado 1 ao estado 2. Nos motores reais, sempre existem algumas inefici\u00eancias que reduzem a efici\u00eancia t\u00e9rmica.<\/li>\n<li>Expans\u00e3o.\u00a0O g\u00e1s (mistura combust\u00edvel-ar) se expande adiabaticamente do estado 3 para o estado 4.<\/li>\n<\/ul>\n<\/li>\n<li><strong>Combust\u00e3o completa<\/strong>\u00a0da mistura combust\u00edvel-ar.<\/li>\n<li><strong>Nenhum trabalho de bombeamento<\/strong>\u00a0.\u00a0Trabalho de bombeamento \u00e9 a diferen\u00e7a entre o trabalho realizado durante o golpe de escape e o trabalho realizado durante o golpe de admiss\u00e3o.\u00a0Nos ciclos reais, h\u00e1 uma diferen\u00e7a de press\u00e3o entre as press\u00f5es de exaust\u00e3o e de entrada.<\/li>\n<li><strong>Sem perda de purga<\/strong>\u00a0.\u00a0A perda de purga \u00e9 causada pela abertura precoce das v\u00e1lvulas de escape.\u00a0Isso resulta em uma perda de produ\u00e7\u00e3o durante o curso de expans\u00e3o.<\/li>\n<li><strong>Sem perda de impacto<\/strong>\u00a0.\u00a0A perda soprada \u00e9 causada pelo vazamento de gases comprimidos atrav\u00e9s de an\u00e9is de pist\u00e3o e outras fendas.<\/li>\n<li><strong>Sem perdas por atrito<\/strong>\u00a0.<\/li>\n<\/ul>\n<p>Essas suposi\u00e7\u00f5es e perdas simplificadoras levam ao fato de que a \u00e1rea fechada (trabalho) do diagrama de pV para um motor real \u00e9 significativamente menor que o tamanho da \u00e1rea (trabalho) envolvida pelo diagrama de pV do ciclo ideal.\u00a0Em outras palavras, o ciclo ideal do motor superestimar\u00e1 o trabalho l\u00edquido e, se os motores funcionarem na mesma velocidade, maior pot\u00eancia produzida pelo motor real em cerca de 20%.<\/p>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<h2>Taxa de compress\u00e3o &#8211; Otto Engine<\/h2>\n<p>A\u00a0<strong>taxa de compress\u00e3o<\/strong>\u00a0,\u00a0<strong>CR<\/strong>\u00a0, \u00e9 definida como a taxa do volume no ponto morto inferior e o volume no ponto morto superior.\u00a0\u00c9 uma das principais caracter\u00edsticas de muitos motores de combust\u00e3o interna.\u00a0Na se\u00e7\u00e3o a seguir, ser\u00e1 mostrado que a\u00a0<strong>taxa de compress\u00e3o<\/strong>\u00a0determina a\u00a0<strong>efici\u00eancia t\u00e9rmica<\/strong>\u00a0do ciclo termodin\u00e2mico usado do motor de combust\u00e3o.\u00a0Em geral, \u00e9 desej\u00e1vel ter uma alta taxa de compress\u00e3o, pois permite que um motor atinja maior efici\u00eancia t\u00e9rmica.<\/p>\n<p>Por exemplo, vamos supor um ciclo Otto com taxa de compress\u00e3o de CR = 10: 1. O volume da c\u00e2mara \u00e9 de 500 cm = 500 x 10\u00a0<sup>-6<\/sup>\u00a0m\u00a0<sup>3<\/sup>\u00a0(0,5 L) antes do curso de compress\u00e3o.\u00a0Para este motor\u00a0<strong>um<\/strong>\u00a0ll necess\u00e1rio volumes s\u00e3o conhecidos:<\/p>\n<ul>\n<li>V\u00a0<sub>1<\/sub>\u00a0= V\u00a0<sub>4<\/sub>\u00a0= V\u00a0<sub>max<\/sub>\u00a0= 500 \u00d7 10\u00a0<sup>-6<\/sup>\u00a0m\u00a0<sup>3<\/sup>\u00a0(0,5l)<\/li>\n<li>V\u00a0<sub>2<\/sub>\u00a0= V\u00a0<sub>3<\/sub>\u00a0= V\u00a0<sub>min<\/sub>\u00a0= V\u00a0<sub>m\u00e1x<\/sub>\u00a0\/ CR = 55,56 \u00d7 10\u00a0<sup>-6<\/sup>\u00a0m\u00a0<sup>3<\/sup><\/li>\n<\/ul>\n<p>Observe que (V\u00a0<sub>max<\/sub>\u00a0&#8211; V\u00a0<sub>min<\/sub>\u00a0) x n\u00famero de cilindros = cilindrada total do motor.<\/p>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<h2>Exemplos de taxas de compress\u00e3o &#8211; Gasolina x Diesel<\/h2>\n<ul>\n<li>A taxa de compacta\u00e7\u00e3o em um motor a gasolina geralmente n\u00e3o ser\u00e1 muito maior que\u00a0<strong>10: 1<\/strong>\u00a0devido a uma poss\u00edvel batida no motor (autoigni\u00e7\u00e3o) e n\u00e3o menor que\u00a0<strong>6: 1<\/strong>\u00a0.<\/li>\n<li>Um Subaru Impreza WRX turbo tem uma taxa de compress\u00e3o de\u00a0<strong>8,0: 1<\/strong>\u00a0.\u00a0Em geral, os motores turboalimentados ou sobrealimentados j\u00e1 possuem ar comprimido na entrada de ar, portanto s\u00e3o geralmente constru\u00eddos com menor taxa de compress\u00e3o.<\/li>\n<li>Um motor Honda S2000 (F22C1) tem uma taxa de compress\u00e3o de\u00a0<strong>11,1: 1<\/strong>\u00a0.<\/li>\n<li>Alguns motores de carros esportivos atmosf\u00e9ricos podem ter uma taxa de compress\u00e3o de at\u00e9\u00a0<strong>12,5: 1<\/strong>\u00a0(por exemplo, Ferrari 458 Italia).<\/li>\n<li>Em 2012, a Mazda lan\u00e7ou novos motores a gasolina sob a marca\u00a0<a href=\"https:\/\/en.wikipedia.org\/wiki\/SkyActiv\">SkyActiv<\/a>\u00a0com uma\u00a0taxa de compress\u00e3o de\u00a0<strong>14: 1<\/strong>\u00a0.\u00a0Para reduzir o risco de bater no motor, o g\u00e1s residual \u00e9 reduzido usando\u00a0<a href=\"https:\/\/en.wikipedia.org\/wiki\/4-2-1_engine_exhaust_systems\">sistemas de escape do motor 4-2-1<\/a>\u00a0, implementando uma cavidade do pist\u00e3o e otimizando a inje\u00e7\u00e3o de combust\u00edvel.<\/li>\n<li>Os motores a diesel t\u00eam uma taxa de compress\u00e3o que normalmente excede 14: 1 e taxas acima de 22: 1 tamb\u00e9m s\u00e3o comuns.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<h2>Efici\u00eancia t\u00e9rmica para o ciclo Otto<\/h2>\n<p>Em geral, a\u00a0<a title=\"Efici\u00eancia t\u00e9rmica\" href=\"https:\/\/www.thermal-engineering.org\/what-is-thermal-efficiency-definition\/\"><strong>efici\u00eancia t\u00e9rmica<\/strong><\/a><a title=\"Efici\u00eancia t\u00e9rmica\" href=\"https:\/\/www.thermal-engineering.org\/what-is-thermal-efficiency-definition\/\">\u00a0,\u00a0<\/a><a title=\"Efici\u00eancia t\u00e9rmica\" href=\"https:\/\/www.thermal-engineering.org\/what-is-thermal-efficiency-definition\/\"><strong><em>\u03b7\u00a0<\/em><\/strong><\/a><a title=\"Efici\u00eancia t\u00e9rmica\" href=\"https:\/\/www.thermal-engineering.org\/what-is-thermal-efficiency-definition\/\"><strong><em><sub>th<\/sub><\/em><\/strong><\/a>\u00a0, de qualquer motor de calor \u00e9 definida como a raz\u00e3o entre o\u00a0<a href=\"https:\/\/www.thermal-engineering.org\/what-is-work-in-thermodynamics-definition\/\">trabalho<\/a>\u00a0que faz,\u00a0<strong>W<\/strong>\u00a0, para o\u00a0<a href=\"https:\/\/www.thermal-engineering.org\/what-is-heat-in-physics-heat-definition\/\">calor<\/a>\u00a0de entrada a uma temperatura elevada, Q\u00a0<sub>H<\/sub>\u00a0.<\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-efficiency-formula-1.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-16945 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-efficiency-formula-1.png\" alt=\"f\u00f3rmula de efici\u00eancia t\u00e9rmica - 1\" width=\"125\" height=\"82\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-efficiency-formula-1.png\" \/><\/a><\/p>\n<p>A\u00a0<strong>efici\u00eancia t\u00e9rmica<\/strong>\u00a0,\u00a0<strong><em>\u03b7\u00a0<\/em><\/strong><strong><em><sub>th<\/sub><\/em><\/strong>\u00a0, representa a fra\u00e7\u00e3o de\u00a0<strong>calor<\/strong>\u00a0,\u00a0<strong>Q\u00a0<\/strong><strong><sub>H<\/sub><\/strong>\u00a0, que \u00e9 convertida\u00a0<strong>em trabalho<\/strong>\u00a0.\u00a0Como a energia \u00e9 conservada de acordo com a\u00a0<a href=\"https:\/\/www.thermal-engineering.org\/what-is-first-law-of-thermodynamics-definition\/\"><strong>primeira lei da termodin\u00e2mica<\/strong><\/a>\u00a0e a energia n\u00e3o pode ser convertida para funcionar completamente, a entrada de calor, Q\u00a0<sub>H<\/sub>\u00a0, deve ser igual ao trabalho realizado, W, mais o calor que deve ser dissipado como\u00a0<strong>calor residual Q\u00a0<\/strong><strong><sub>C<\/sub><\/strong>\u00a0no meio Ambiente.\u00a0Portanto, podemos reescrever a f\u00f3rmula da efici\u00eancia t\u00e9rmica como:<\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-efficiency-formula-2.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-16944 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-efficiency-formula-2.png\" alt=\"f\u00f3rmula de efici\u00eancia t\u00e9rmica - 2\" width=\"352\" height=\"83\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-efficiency-formula-2.png\" \/><\/a><\/p>\n<p>O calor absorvido ocorre durante a combust\u00e3o da mistura combust\u00edvel-ar, quando a fa\u00edsca ocorre, aproximadamente a volume constante.\u00a0Como durante um\u00a0<a title=\"Processo Isoc\u00f3rico - Processo Isom\u00e9trico\" href=\"https:\/\/www.thermal-engineering.org\/what-is-isochoric-process-isometric-process-definition\/\">processo isoc\u00f3rico<\/a>\u00a0n\u00e3o h\u00e1 trabalho realizado pelo sistema ou sobre ele, a\u00a0<strong>primeira lei da termodin\u00e2mica<\/strong>\u00a0determina\u00a0<em>\u2206U = \u2206Q.\u00a0<\/em>Portanto, o calor adicionado e rejeitado \u00e9 dado por:<\/p>\n<p><strong>Q\u00a0<sub>add<\/sub>\u00a0= mc\u00a0<sub>v<\/sub>\u00a0(T\u00a0<sub>3<\/sub>\u00a0&#8211; T\u00a0<sub>2<\/sub>\u00a0)<\/strong><\/p>\n<p><strong>Q\u00a0<sub>out<\/sub>\u00a0= mc\u00a0<sub>v<\/sub>\u00a0(T\u00a0<sub>4<\/sub>\u00a0&#8211; T\u00a0<sub>1<\/sub>\u00a0)<\/strong><\/p>\n<p>Substituindo essas express\u00f5es pelo calor adicionado e rejeitado na express\u00e3o por efici\u00eancia t\u00e9rmica, obt\u00e9m-se:<\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Otto-cycle-efficiency-equation.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-17557 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Otto-cycle-efficiency-equation.png\" alt=\"Ciclo Otto - efici\u00eancia - equa\u00e7\u00e3o\" width=\"193\" height=\"65\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Otto-cycle-efficiency-equation.png\" \/><\/a><\/p>\n<p>Podemos simplificar a express\u00e3o acima usando o fato de que os processos\u00a0<strong>1 \u2192 2<\/strong>\u00a0e de\u00a0<strong>3 \u2192 4<\/strong>\u00a0s\u00e3o adiab\u00e1ticos e, para um processo adiab\u00e1tico, a seguinte f\u00f3rmula p, V, T \u00e9 v\u00e1lida:<\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/adiabatic-process-formula.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-17558 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/adiabatic-process-formula.png\" alt=\"processo adiab\u00e1tico - f\u00f3rmula\" width=\"154\" height=\"84\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/adiabatic-process-formula.png\" \/><\/a><\/p>\n<p>Pode-se derivar que:<\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/adiabatic-process-formula2.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-17559 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/adiabatic-process-formula2.png\" alt=\"processo adiab\u00e1tico - formula2\" width=\"193\" height=\"77\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/adiabatic-process-formula2.png\" \/><\/a><\/p>\n<p>Nesta equa\u00e7\u00e3o, a\u00a0<strong>raz\u00e3o V\u00a0<sub>1<\/sub>\u00a0\/ V\u00a0<sub>2<\/sub><\/strong>\u00a0\u00e9 conhecida como\u00a0<strong>taxa de compress\u00e3o, CR<\/strong>\u00a0.\u00a0Quando reescrevemos a express\u00e3o para efici\u00eancia t\u00e9rmica usando a taxa de compress\u00e3o, conclu\u00edmos que a\u00a0efici\u00eancia t\u00e9rmica do\u00a0<strong>ciclo Otto padr\u00e3o<\/strong>\u00a0do\u00a0<strong>ar<\/strong>\u00a0\u00e9 uma fun\u00e7\u00e3o da\u00a0<strong>taxa<\/strong>\u00a0de\u00a0<strong>compress\u00e3o<\/strong>\u00a0e\u00a0\u00a0<strong>\u03ba = c\u00a0<\/strong><strong><sub>p<\/sub><\/strong><strong>\u00a0\/ c\u00a0<\/strong><strong><sub>v<\/sub><\/strong>\u00a0.<\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-efficiency-Otto-Cycle-Compression-ratio.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-17560 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-efficiency-Otto-Cycle-Compression-ratio.png\" alt=\"efici\u00eancia t\u00e9rmica - Ciclo Otto - Taxa de compress\u00e3o\" width=\"570\" height=\"80\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-efficiency-Otto-Cycle-Compression-ratio.png\" \/><\/a><\/p>\n<figure id=\"attachment_17561\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-17561\"><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-efficiency-Otto-Cycle-Engine.png\"><img loading=\"lazy\" class=\"size-medium wp-image-17561 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-efficiency-Otto-Cycle-Engine-300x256.png\" alt=\"efici\u00eancia t\u00e9rmica - Otto Cycle - Motor\" width=\"300\" height=\"256\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/thermal-efficiency-Otto-Cycle-Engine-300x256.png\" \/><\/a><figcaption id=\"caption-attachment-17561\" class=\"wp-caption-text\">Efici\u00eancia t\u00e9rmica para o ciclo Otto &#8211; \u03ba = 1,4<\/figcaption><\/figure>\n<p>\u00c9 uma conclus\u00e3o muito \u00fatil, porque \u00e9 desej\u00e1vel alcan\u00e7ar uma\u00a0<strong>alta taxa de compress\u00e3o<\/strong>\u00a0para extrair mais energia mec\u00e2nica de uma dada massa de mistura ar-combust\u00edvel.\u00a0Uma taxa de compress\u00e3o mais alta permite alcan\u00e7ar a mesma temperatura de combust\u00e3o com menos combust\u00edvel, proporcionando um ciclo de expans\u00e3o mais longo.\u00a0Isso cria mais pot\u00eancia mec\u00e2nica e\u00a0<strong>reduz a temperatura do escapamento<\/strong>\u00a0.\u00a0A redu\u00e7\u00e3o da temperatura de exaust\u00e3o causa a diminui\u00e7\u00e3o da energia rejeitada na atmosfera.\u00a0Essa rela\u00e7\u00e3o \u00e9 mostrada na figura para \u03ba = 1,4, representando o ar ambiente.<\/p>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<h2>Autoigni\u00e7\u00e3o &#8211; Limite para taxa de compress\u00e3o<\/h2>\n<p>Em motores a gasolina comuns, a\u00a0<strong>taxa de compress\u00e3o<\/strong>\u00a0tem seus limites.\u00a0A taxa de compacta\u00e7\u00e3o em um motor a gasolina geralmente n\u00e3o ser\u00e1 muito maior que\u00a0<strong>10: 1<\/strong>\u00a0devido a uma poss\u00edvel\u00a0<strong>batida no<\/strong>\u00a0motor\u00a0(\u00a0<strong>autoigni\u00e7\u00e3o<\/strong>\u00a0) e n\u00e3o menor que\u00a0<strong>6: 1<\/strong>\u00a0.\u00a0Taxas de compress\u00e3o mais altas, no entanto, sujeitam os motores a gasolina a bater ao motor, causados \u200b\u200bpela\u00a0<strong>autoigni\u00e7\u00e3o de uma mistura n\u00e3o queimada<\/strong>\u00a0, se for usado combust\u00edvel com menor octanagem.\u00a0A mistura n\u00e3o queimada pode se auto-incendiar, detonando apenas da press\u00e3o e do calor, em vez de inflamar da vela exatamente no momento certo.\u00a0A\u00a0<strong>batida do motor<\/strong>\u00a0pode ser reduzida usando\u00a0<strong>combust\u00edvel de alta octanagem<\/strong>, o que aumenta a\u00a0<strong>resist\u00eancia<\/strong>\u00a0da gasolina\u00a0<strong>\u00e0 auto-igni\u00e7\u00e3o<\/strong>\u00a0.\u00a0Quanto maior o n\u00famero de octanas, maior a compress\u00e3o do combust\u00edvel antes de detonar (acender).\u00a0Como a temperatura atingida pela mistura combust\u00edvel-ar durante a compress\u00e3o aumenta \u00e0 medida que a taxa de compress\u00e3o aumenta, a probabilidade de auto-igni\u00e7\u00e3o aumenta com a taxa de compress\u00e3o.\u00a0A autoigni\u00e7\u00e3o pode reduzir a efici\u00eancia ou danificar o motor se n\u00e3o houver sensores de batida para modificar o tempo de igni\u00e7\u00e3o.<\/p>\n<p>Taxas de compress\u00e3o mais altas podem ser alcan\u00e7adas em\u00a0<strong>motores a diesel<\/strong>\u00a0(tamb\u00e9m chamados de\u00a0<strong>motores de igni\u00e7\u00e3o por compress\u00e3o<\/strong>\u00a0), porque eles n\u00e3o comprimem o combust\u00edvel, mas comprimem apenas o ar e injetam combust\u00edvel no ar que foi aquecido por compress\u00e3o.\u00a0As taxas de compress\u00e3o na faixa de 12 a 20 s\u00e3o t\u00edpicas para motores a diesel.\u00a0A maior expans\u00e3o nos motores diesel significa que eles rejeitam menos calor em seus escapamentos mais frios.\u00a0A maior taxa de compress\u00e3o (maior expans\u00e3o) e a temperatura de pico mais alta fazem com que os motores a diesel atinjam maior efici\u00eancia t\u00e9rmica.<\/p>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<h2>Press\u00e3o Efetiva M\u00e9dia &#8211; MEP<\/h2>\n<figure id=\"attachment_17562\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-17562\"><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Mean-Effective-Pressure-Otto-cycle-chart.png\"><img loading=\"lazy\" class=\"size-medium wp-image-17562 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Mean-Effective-Pressure-Otto-cycle-chart-300x250.png\" alt=\"O MEP \u00e9 uma medida muito \u00fatil da capacidade de um motor para executar um trabalho independente do deslocamento do motor. \" width=\"300\" height=\"250\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Mean-Effective-Pressure-Otto-cycle-chart-300x250.png\" \/><\/a><figcaption id=\"caption-attachment-17562\" class=\"wp-caption-text\">O MEP \u00e9 uma medida muito \u00fatil da capacidade de um motor para executar um trabalho independente do deslocamento do motor.<\/figcaption><\/figure>\n<p>Um par\u00e2metro usado pelos engenheiros para descrever o desempenho dos motores de pist\u00e3o alternativo \u00e9 conhecido como\u00a0<strong>press\u00e3o efetiva m\u00e9dia<\/strong>\u00a0, ou\u00a0<strong>MEP<\/strong>\u00a0.\u00a0<strong>O MEP<\/strong>\u00a0\u00e9 uma medida muito \u00fatil da capacidade de um motor para executar um trabalho independente do deslocamento do motor.\u00a0Existem v\u00e1rios tipos de MEP.\u00a0Esses MEPs s\u00e3o definidos pela medi\u00e7\u00e3o da localiza\u00e7\u00e3o e pelo m\u00e9todo de c\u00e1lculo (por exemplo, BMEP ou IMEP).<\/p>\n<p>Em geral, a\u00a0<strong>press\u00e3o efetiva m\u00e9dia<\/strong>\u00a0\u00e9 a press\u00e3o constante te\u00f3rica que, se ela atuasse no pist\u00e3o durante o curso de for\u00e7a, produziria o mesmo trabalho l\u00edquido como realmente desenvolvido em um ciclo completo.\u00a0O MEP pode ser definido como:<\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/mean-effective-pressure-definition.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-17565 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/mean-effective-pressure-definition.png\" alt=\"press\u00e3o efetiva m\u00e9dia - defini\u00e7\u00e3o\" width=\"300\" height=\"63\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/mean-effective-pressure-definition.png\" \/><\/a><\/p>\n<p>Por exemplo, a\u00a0<strong>press\u00e3o efetiva m\u00e9dia<\/strong>\u00a0l\u00edquida\u00a0<strong>indicada<\/strong>\u00a0, conhecida como\u00a0<strong>IMEP\u00a0<sub>n<\/sub><\/strong>\u00a0\u00e9 igual \u00e0 press\u00e3o efetiva m\u00e9dia calculada a partir da press\u00e3o no cilindro (deve haver essa medi\u00e7\u00e3o) durante todo o ciclo do motor.\u00a0Observe que \u00e9 720 \u00b0 para um motor a quatro tempos e 360 \u200b\u200b\u00b0 para um motor a dois tempos.<\/p>\n<p>Alguns exemplos:<\/p>\n<ul>\n<li>O MEP de um motor a gasolina atmosf\u00e9rico pode variar de 8 a 11 bar na regi\u00e3o de torque m\u00e1ximo.<\/li>\n<li>O MEP de um motor a gasolina turbo pode variar de 12 a 17 bar.<\/li>\n<li>O MEP de um motor diesel atmosf\u00e9rico pode variar de 7 a 9 bar.<\/li>\n<li>MEP de um motor diesel turboalimentado pode variar de 14 a 18 bar<\/li>\n<\/ul>\n<p>Por exemplo, um motor a gasolina a quatro tempos produzindo 200 N \u00b7 m a partir de 2 litros de deslocamento possui um MPE de (4\u03c0) (200 N \u00b7 m) \/ (0,002 m\u00b3) = 1256000 Pa = 12 bar.\u00a0Como pode ser visto, o MEP \u00e9 uma\u00a0<strong>caracter\u00edstica<\/strong>\u00a0\u00fatil\u00a0<strong>de um motor<\/strong>\u00a0.\u00a0Para dois motores de igual volume de cilindrada, aquele com um\u00a0<strong>MEP maior<\/strong>\u00a0produziria o\u00a0<strong>maior trabalho l\u00edquido<\/strong>\u00a0e, se os motores funcionassem na mesma velocidade,\u00a0<strong>maior pot\u00eancia<\/strong>\u00a0.<\/p>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spacer\"><\/div>\n<h2>Ciclo Otto &#8211; Problema com solu\u00e7\u00e3o<\/h2>\n<p>Vamos assumir o\u00a0<a title=\"Ciclo Otto - Otto Engine\" href=\"https:\/\/www.thermal-engineering.org\/what-is-otto-cycle-otto-engine-definition\/\"><strong>ciclo Otto<\/strong><\/a>\u00a0, que \u00e9 um dos\u00a0<strong>ciclos termodin\u00e2micos<\/strong>\u00a0mais comuns\u00a0encontrados em\u00a0<strong>motores de autom\u00f3veis<\/strong>\u00a0.\u00a0Um dos principais par\u00e2metros desses motores \u00e9 a mudan\u00e7a de volumes entre o ponto morto superior (TDC) e o ponto morto inferior (BDC).\u00a0A propor\u00e7\u00e3o desses volumes (\u00a0<em>V\u00a0<\/em><em><sub>1<\/sub><\/em><em>\u00a0\/ V\u00a0<\/em><em><sub>2<\/sub><\/em>\u00a0) \u00e9 conhecida como\u00a0<strong>taxa de compress\u00e3o<\/strong>\u00a0.<\/p>\n<p>A\u00a0<strong>taxa de compacta\u00e7\u00e3o<\/strong>\u00a0em um motor a gasolina geralmente n\u00e3o ser\u00e1 muito maior que 10: 1 devido a uma poss\u00edvel batida no motor (autoigni\u00e7\u00e3o) e n\u00e3o menor que 6: 1.\u00a0Por exemplo, alguns motores de carros esportivos podem ter taxa de compress\u00e3o de at\u00e9 12,5: 1 (por exemplo, Ferrari 458 Italia).<\/p>\n<figure id=\"attachment_17461\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-17461\"><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Otto-Cycle-PV-Diagram.png\"><img loading=\"lazy\" class=\"size-medium wp-image-17461 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Otto-Cycle-PV-Diagram-300x245.png\" alt=\"Otto Cycle - Diagrama PV\" width=\"300\" height=\"245\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Otto-Cycle-PV-Diagram-300x245.png\" \/><\/a><figcaption id=\"caption-attachment-17461\" class=\"wp-caption-text\">diagrama pV do ciclo Otto.\u00a0A \u00e1rea delimitada pelo caminho completo do ciclo representa o trabalho total que pode ser realizado durante um ciclo.<\/figcaption><\/figure>\n<p>Neste exemplo, vamos assumir um ciclo Otto com\u00a0<strong>taxa<\/strong>\u00a0de\u00a0<strong>compress\u00e3o<\/strong>\u00a0de\u00a0<strong>CR = 9: 1<\/strong>\u00a0.\u00a0O ar de admiss\u00e3o \u00e9 de 100 kPa = 1 bar, 20 \u00b0 C e o volume da c\u00e2mara \u00e9 de 500 cm\u00b3 antes do curso de compress\u00e3o.\u00a0A temperatura no final da\u00a0<a title=\"Processo Adiab\u00e1tico\" href=\"https:\/\/www.thermal-engineering.org\/what-is-adiabatic-process-definition\/\">expans\u00e3o adiab\u00e1tica<\/a>\u00a0\u00e9 T\u00a0<sub>4<\/sub>\u00a0= 800 K.<\/p>\n<ul>\n<li>Capacidade t\u00e9rmica espec\u00edfica a press\u00e3o constante do ar \u00e0 press\u00e3o atmosf\u00e9rica e \u00e0 temperatura ambiente:\u00a0<strong>c\u00a0<\/strong><strong><sub>p<\/sub><\/strong><strong>\u00a0= 1,01 kJ \/ kgK.<\/strong><\/li>\n<li>Capacidade t\u00e9rmica espec\u00edfica a um volume constante de ar \u00e0 press\u00e3o atmosf\u00e9rica e \u00e0 temperatura ambiente:\u00a0<strong>c\u00a0<\/strong><strong><sub>v<\/sub><\/strong><strong>\u00a0= 0,718 kJ \/ kgK.<\/strong><\/li>\n<li><strong>\u03ba = c\u00a0<\/strong><strong><sub>p<\/sub><\/strong><strong>\u00a0\/ c\u00a0<\/strong><strong><sub>v<\/sub><\/strong><strong>\u00a0= 1,4<\/strong><\/li>\n<\/ul>\n<p><strong>Calcular:<\/strong><\/p>\n<ol>\n<li><strong>a massa de entrada de ar<\/strong><\/li>\n<li><strong>a temperatura T\u00a0<\/strong><strong><sub>3<\/sub><\/strong><\/li>\n<li><strong>a press\u00e3o p\u00a0<\/strong><strong><sub>3<\/sub><\/strong><\/li>\n<li><strong>a quantidade de calor adicionada pela queima da mistura combust\u00edvel-ar<\/strong><\/li>\n<li><strong>a efici\u00eancia t\u00e9rmica deste ciclo<\/strong><\/li>\n<li><strong>o deputado<\/strong><\/li>\n<\/ol>\n<p><strong>Solu\u00e7\u00e3o:<\/strong><\/p>\n<p>1)\u00a0\u00a0<strong>a massa de entrada de ar<\/strong><\/p>\n<p>No in\u00edcio dos c\u00e1lculos, temos que determinar a quantidade de g\u00e1s no cilindro antes do curso de compress\u00e3o.\u00a0Usando a lei do g\u00e1s ideal, podemos encontrar a massa:<\/p>\n<p><strong><em>pV = mR\u00a0<\/em><em><sub>espec\u00edfico<\/sub><\/em><em>\u00a0T<\/em><\/strong><\/p>\n<p>Onde:<\/p>\n<ul>\n<li><em>p<\/em>\u00a0\u00e9 a\u00a0<a title=\"Press\u00e3o absoluta\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/thermodynamic-properties\/what-is-pressure-physics\/absolute-pressure\/\">press\u00e3o absoluta<\/a>\u00a0do g\u00e1s<\/li>\n<li><em>m<\/em>\u00a0\u00e9 a massa da subst\u00e2ncia<\/li>\n<li><em>T<\/em>\u00a0\u00e9 a\u00a0<a title=\"Escala Kelvin - Temperatura Absoluta\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/thermodynamic-properties\/what-is-temperature-physics\/kelvin-scale-absolute-temperature\/\">temperatura absoluta<\/a><\/li>\n<li><em>V<\/em>\u00a0\u00e9 o volume<\/li>\n<li><em>R\u00a0<\/em><em><sub>espec\u00edfico<\/sub><\/em>\u00a0\u00a0\u00e9 a constante de g\u00e1s espec\u00edfica, igual \u00e0 constante de g\u00e1s universal dividida pela massa molar (M) do g\u00e1s ou mistura.\u00a0Para ar seco R\u00a0<sub>espec\u00edfico<\/sub>\u00a0= 287,1 J.kg\u00a0<sup>-1<\/sup>\u00a0.K\u00a0<sup>-1<\/sup>\u00a0.<\/li>\n<\/ul>\n<p>Portanto<\/p>\n<p><strong>m<\/strong>\u00a0= p\u00a0<sub>1<\/sub>\u00a0V\u00a0<sub>1<\/sub>\u00a0\/ R\u00a0<sub>espec\u00edfico<\/sub>\u00a0T\u00a0<sub>1<\/sub>\u00a0= (100000 \u00d7 500 \u00d7 10\u00a0<sup>-6<\/sup>\u00a0) \/ (287,1 \u00d7 293) =\u00a0<strong>5,95 \u00d7 10\u00a0<\/strong><strong><sup>-4<\/sup><\/strong><strong>\u00a0kg<\/strong><\/p>\n<p><strong>Nesse problema, todos os volumes s\u00e3o conhecidos:<\/strong><\/p>\n<ul>\n<li>V\u00a0<sub>1<\/sub>\u00a0= V\u00a0<sub>4<\/sub>\u00a0= V\u00a0<sub>max\u00a0<\/sub><strong>=<\/strong>\u00a0500 \u00d7 10\u00a0<sup>-6<\/sup>\u00a0m\u00a0<sup>3<\/sup>\u00a0(0,5l)<\/li>\n<li>V\u00a0<sub>2<\/sub>\u00a0= V\u00a0<sub>3<\/sub>\u00a0= V\u00a0<sub>min<\/sub>\u00a0= V\u00a0<sub>m\u00e1x<\/sub>\u00a0\/ CR = 55,56 \u00d7 10\u00a0<sup>-6<\/sup>\u00a0m\u00a0<sup>3<\/sup><\/li>\n<\/ul>\n<p>Observe que (V\u00a0<sub>max<\/sub>\u00a0&#8211; V\u00a0<sub>min<\/sub>\u00a0) x n\u00famero de cilindros = cilindrada total do motor.<\/p>\n<p>2)\u00a0\u00a0<strong>a temperatura T\u00a0<\/strong><strong><sub>3<\/sub><\/strong><\/p>\n<p>Como o processo \u00e9 adiab\u00e1tico, podemos usar a seguinte rela\u00e7\u00e3o p, V, T para\u00a0<a title=\"Processo Adiab\u00e1tico\" href=\"https:\/\/www.thermal-engineering.org\/what-is-adiabatic-process-definition\/\">processos adiab\u00e1ticos<\/a>\u00a0:<\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/adiabatic-formula-example.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-17563 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/adiabatic-formula-example.png\" alt=\"f\u00f3rmula adiab\u00e1tica - exemplo\" width=\"155\" height=\"78\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/adiabatic-formula-example.png\" \/><\/a><\/p>\n<p>portanto<\/p>\n<p><strong>T\u00a0<sub>3<\/sub><\/strong>\u00a0= T\u00a0<sub>4<\/sub>\u00a0.\u00a0CR\u00a0<sup>k &#8211; 1<\/sup>\u00a0= 800.\u00a09\u00a0<sup>0,4<\/sup>\u00a0=\u00a0<strong>1926 K<\/strong><\/p>\n<p>3)\u00a0\u00a0<strong>a press\u00e3o p\u00a0<\/strong><strong><sub>3<\/sub><\/strong><\/p>\n<p>Novamente, podemos usar a\u00a0<a title=\"Lei do g\u00e1s ideal\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/ideal-gas-law\/\">lei do g\u00e1s ideal<\/a>\u00a0para encontrar a press\u00e3o no in\u00edcio do curso de for\u00e7a como:<\/p>\n<p><strong>p\u00a0<\/strong><strong><sub>3<\/sub><\/strong>\u00a0= mR\u00a0<sub>espec\u00edfico<\/sub>\u00a0T\u00a0<sub>3<\/sub>\u00a0\/ V\u00a0<sub>3<\/sub>\u00a0= 5,95 \u00d7 10\u00a0<sup>-4<\/sup>\u00a0x 287,1 x 1926 \/ 55,56 \u00d7 10\u00a0<sup>-6<\/sup>\u00a0= 5920000 Pa =\u00a0<strong>59,2 bar<\/strong><\/p>\n<p>4)\u00a0\u00a0<strong>a quantidade de calor adicionada<\/strong><\/p>\n<p>Para calcular a quantidade de calor adicionada pela queima da mistura combust\u00edvel-ar,\u00a0<sub>adicione<\/sub>\u00a0Q\u00a0, temos que usar a\u00a0<a title=\"Primeira Lei da Termodin\u00e2mica\" href=\"https:\/\/www.thermal-engineering.org\/what-is-first-law-of-thermodynamics-definition\/\">primeira lei da termodin\u00e2mica<\/a>\u00a0para\u00a0<a title=\"Processo Isoc\u00f3rico - Processo Isom\u00e9trico\" href=\"https:\/\/www.thermal-engineering.org\/what-is-isochoric-process-isometric-process-definition\/\">processos isoc\u00f3ricos<\/a>\u00a0, que declara Q\u00a0<sub>add<\/sub>\u00a0= \u2206U, portanto:<\/p>\n<p><strong>Q\u00a0<sub>add<\/sub>\u00a0= mc\u00a0<sub>v<\/sub>\u00a0(T\u00a0<sub>3<\/sub>\u00a0&#8211; T\u00a0<sub>2<\/sub>\u00a0)<\/strong><\/p>\n<p>a temperatura no final do curso de compress\u00e3o pode ser determinada usando a rela\u00e7\u00e3o p, V, T para processos adiab\u00e1ticos entre os pontos\u00a0<strong>1 \u2192 2.<\/strong><\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/adiabatic-process-formula.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-17558 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/adiabatic-process-formula.png\" alt=\"processo adiab\u00e1tico - f\u00f3rmula\" width=\"154\" height=\"84\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/adiabatic-process-formula.png\" \/><\/a><\/p>\n<p><strong>T\u00a0<sub>2<\/sub><\/strong>\u00a0= T\u00a0<sub>1<\/sub>\u00a0.\u00a0CR\u00a0<sup>k &#8211; 1<\/sup>\u00a0= 293.\u00a09\u00a0<sup>0,4<\/sup>\u00a0=\u00a0<strong>706 K<\/strong><\/p>\n<p>ent\u00e3o<\/p>\n<p><strong>Q\u00a0<\/strong><strong><sub>add<\/sub><\/strong>\u00a0= mc\u00a0<sub>v<\/sub>\u00a0(T\u00a0<sub>3<\/sub>\u00a0&#8211; T\u00a0<sub>2<\/sub>\u00a0) = 5,95 \u00d7 10\u00a0<sup>-4<\/sup>\u00a0x 718 x 1220 =\u00a0<strong>521,2 J<\/strong><\/p>\n<p>5)\u00a0\u00a0<strong>a efici\u00eancia t\u00e9rmica<\/strong><\/p>\n<p><a title=\"Efici\u00eancia t\u00e9rmica\" href=\"https:\/\/www.thermal-engineering.org\/what-is-thermal-efficiency-definition\/\"><strong>Efici\u00eancia t\u00e9rmica<\/strong><\/a>\u00a0para um ciclo Otto:<\/p>\n<p>Como foi derivado na se\u00e7\u00e3o anterior, a efici\u00eancia t\u00e9rmica de um ciclo Otto \u00e9 uma fun\u00e7\u00e3o da taxa de compress\u00e3o e \u03ba:<\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Otto-cycle-efficiency-example.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-17564 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Otto-cycle-efficiency-example.png\" alt=\"Ciclo Otto - efici\u00eancia - exemplo\" width=\"309\" height=\"172\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/Otto-cycle-efficiency-example.png\" \/><\/a><\/p>\n<p>6)\u00a0\u00a0<strong>a press\u00e3o efetiva m\u00e9dia<\/strong><\/p>\n<p>O\u00a0<strong>MEP<\/strong>\u00a0foi definido como:<\/p>\n<p><a href=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/mean-effective-pressure-definition.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-17565 lazy-loaded\" src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/mean-effective-pressure-definition.png\" alt=\"press\u00e3o efetiva m\u00e9dia - defini\u00e7\u00e3o\" width=\"300\" height=\"63\" data-lazy-type=\"image\" data-src=\"https:\/\/thermal-engineering.org\/wp-content\/uploads\/2019\/05\/mean-effective-pressure-definition.png\" \/><\/a><\/p>\n<p>Nesta equa\u00e7\u00e3o, o volume de deslocamento \u00e9 igual a V\u00a0<sub>max<\/sub>\u00a0&#8211; V\u00a0<sub>min<\/sub>\u00a0.\u00a0O trabalho l\u00edquido para um ciclo pode ser calculado usando o calor adicionado e a efici\u00eancia t\u00e9rmica:<\/p>\n<p><strong><em>W\u00a0<\/em><\/strong><strong><em><sub>net<\/sub><\/em><\/strong><em>\u00a0=\u00a0<\/em><em>Q\u00a0<\/em><em><sub>add<\/sub><\/em><em>\u00a0.\u00a0\u03b7\u00a0<\/em><em><sub>Otto<\/sub><\/em><em>\u00a0=\u00a0<\/em><em>521,2 x 0,5847 = 304,7\u00a0<strong>J<\/strong><\/em><br \/>\n<strong><em>MEP<\/em><\/strong><em>\u00a0= 304,7 \/ (<\/em>\u00a0500 \u00d7 10<sup>\u00a0-6<\/sup>\u00a0&#8211; 55,56 \u00d7 10<sup>\u00a0-6\u00a0<\/sup><em>) = 685,6 kPa =\u00a0<strong>6,856 bar<\/strong><\/em><\/p>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights lgc-first lgc-last\">\n<div class=\"inside-grid-column\"><\/div>\n<\/div>\n<\/div>\n<p>&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;.<\/p>\n<p>Este artigo \u00e9 baseado na tradu\u00e7\u00e3o autom\u00e1tica do artigo original em ingl\u00eas. Para mais informa\u00e7\u00f5es, consulte o artigo em ingl\u00eas. Voc\u00ea pode nos ajudar. Se voc\u00ea deseja corrigir a tradu\u00e7\u00e3o, envie-a para: translations@nuclear-power.com ou preencha o formul\u00e1rio de tradu\u00e7\u00e3o on-line. Agradecemos sua ajuda, atualizaremos a tradu\u00e7\u00e3o o mais r\u00e1pido poss\u00edvel. Obrigado.<\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>O ciclo do mecanismo Otto \u00e9 chamado de ciclo Otto. \u00c9 um dos ciclos termodin\u00e2micos mais comuns que podem ser encontrados em motores de autom\u00f3veis. Ciclo de Otto &#8211; Motor de Otto \u00a0Ciclo de Otto &#8211; Motor de Otto Em 1876, um engenheiro alem\u00e3o,\u00a0Nikolaus August Otto,\u00a0avan\u00e7ou no estudo de motores t\u00e9rmicos construindo o primeiro motor &#8230; <a title=\"O que \u00e9 o Ciclo de Otto &#8211; Motor de Otto &#8211; Defini\u00e7\u00e3o\" class=\"read-more\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-o-ciclo-otto-otto-engine-definicao\/\" aria-label=\"More on O que \u00e9 o Ciclo de Otto &#8211; Motor de Otto &#8211; Defini\u00e7\u00e3o\">Ler mais<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[14],"tags":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v15.4 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>O que \u00e9 o Ciclo de Otto - Motor de Otto - Defini\u00e7\u00e3o<\/title>\n<meta name=\"description\" content=\"O ciclo do mecanismo Otto \u00e9 chamado de ciclo Otto. \u00c9 um dos ciclos termodin\u00e2micos mais comuns que podem ser encontrados em motores de autom\u00f3veis. 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