{"id":47999,"date":"2019-11-07T17:14:50","date_gmt":"2019-11-07T16:14:50","guid":{"rendered":"https:\/\/www.thermal-engineering.org\/o-que-e-o-motor-a-gasolina-a-quatro-tempos-otto-cycle-definicao\/"},"modified":"2020-01-26T17:46:39","modified_gmt":"2020-01-26T16:46:39","slug":"o-que-e-o-motor-a-gasolina-a-quatro-tempos-otto-cycle-definicao","status":"publish","type":"post","link":"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-o-motor-a-gasolina-a-quatro-tempos-otto-cycle-definicao\/","title":{"rendered":"O que \u00e9 o motor a gasolina a quatro tempos &#8211; Otto Cycle &#8211; Defini\u00e7\u00e3o"},"content":{"rendered":"<div class=\"su-quote su-quote-style-default\">\n<div class=\"su-quote-inner su-clearfix\">Motor a gasolina a quatro tempos &#8211; Otto Cycle.\u00a0Como funciona o motor a quatro tempos.\u00a0Um curso refere-se ao curso completo do pist\u00e3o ao longo do cilindro, em qualquer dire\u00e7\u00e3o.\u00a0Engenharia T\u00e9rmica<\/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>Ciclo Otto &#8211; Otto Engine<\/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<h2>Otto Cycle &#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<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<p><strong><span>O motor de quatro tempos compreende:<\/span><\/strong><\/p>\n<ul>\n<li><strong><span>o curso de admiss\u00e3o &#8211;<\/span><\/strong><span>\u00a0O pist\u00e3o se move do ponto morto superior (TDC) para o ponto morto inferior (BDC) e o ciclo passa pelos pontos\u00a0<\/span><strong><span>0 \u2192 1.<\/span><\/strong><span>\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.<\/span><\/li>\n<li><strong><span>o curso de compress\u00e3o &#8211;<\/span><\/strong><span>\u00a0O pist\u00e3o se move do ponto morto inferior (BDC) para o ponto morto superior (TDC) e o ciclo passa pelos pontos\u00a0<\/span><strong><span>1 \u2192 2.\u00a0<\/span><\/strong><span>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.<\/span><\/li>\n<li><strong><span>o curso de for\u00e7a &#8211;<\/span><\/strong><span>\u00a0O pist\u00e3o se move do ponto morto superior (TDC) para o ponto morto inferior (BDC) e o ciclo passa pelos pontos\u00a0<\/span><strong><span>2 \u2192 3 \u2192 4.<\/span><\/strong><span>\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.<\/span><\/li>\n<li><strong><span>o curso de escape.\u00a0<\/span><\/strong><span>O pist\u00e3o se move do ponto morto inferior (BDC) para o ponto morto superior (TDC) e o ciclo passa pelos pontos\u00a0<\/span><strong><span>4 \u2192 1 \u2192 0.<\/span><\/strong><span>\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.<\/span><\/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><span>Compara\u00e7\u00e3o dos ciclos Otto reais e ideais<\/span><\/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><span>Nesta se\u00e7\u00e3o, \u00e9 mostrado um\u00a0<\/span><strong><span>ciclo Otto ideal,<\/span><\/strong><span>\u00a0no qual existem muitas\u00a0<\/span><strong><span>suposi\u00e7\u00f5es<\/span><\/strong><span>\u00a0diferentes do\u00a0<\/span><strong><span>ciclo Otto real<\/span><\/strong><span>\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:<\/span><\/p>\n<ul>\n<li><strong><span>Ciclo fechado.\u00a0<\/span><\/strong><span>\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<\/span><sub><span>out<\/span><\/sub><span>\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.<\/span><\/li>\n<li><strong><span>Adi\u00e7\u00e3o instant\u00e2nea de calor<\/span><\/strong><span>\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.<\/span><\/li>\n<li><strong><span>Sem transfer\u00eancia de calor (adiab\u00e1tico)<\/span><\/strong>\n<ul>\n<li><span>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.<\/span><\/li>\n<li><span>Expans\u00e3o.\u00a0O g\u00e1s (mistura combust\u00edvel-ar) se expande adiabaticamente do estado 3 para o estado 4.<\/span><\/li>\n<\/ul>\n<\/li>\n<li><strong><span>Combust\u00e3o completa<\/span><\/strong><span>\u00a0da mistura combust\u00edvel-ar.<\/span><\/li>\n<li><strong><span>Nenhum trabalho de bombeamento<\/span><\/strong><span>\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.<\/span><\/li>\n<li><strong><span>Sem perda de purga<\/span><\/strong><span>\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.<\/span><\/li>\n<li><strong><span>Sem perda de impacto<\/span><\/strong><span>\u00a0.\u00a0A perda soprada \u00e9 causada pelo vazamento de gases comprimidos atrav\u00e9s de an\u00e9is de pist\u00e3o e outras fendas.<\/span><\/li>\n<li><strong><span>Sem perdas por atrito<\/span><\/strong><span>\u00a0.<\/span><\/li>\n<\/ul>\n<p><span>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%.<\/span><\/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><span>Taxa de compress\u00e3o &#8211; Otto Engine<\/span><\/h2>\n<p><span>A\u00a0<\/span><strong><span>taxa de compress\u00e3o<\/span><\/strong><span>\u00a0,\u00a0<\/span><strong><span>CR<\/span><\/strong><span>\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<\/span><strong><span>taxa de compress\u00e3o<\/span><\/strong><span>\u00a0determina a\u00a0<\/span><strong><span>efici\u00eancia t\u00e9rmica<\/span><\/strong><span>\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.<\/span><\/p>\n<p><span>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<\/span><sup><span>-6<\/span><\/sup><span>\u00a0m\u00a0<\/span><sup><span>3<\/span><\/sup><span>\u00a0(0,5 L) antes do curso de compress\u00e3o.\u00a0Para este motor\u00a0<\/span><strong><span>um<\/span><\/strong><span>\u00a0ll necess\u00e1rio volumes s\u00e3o conhecidos:<\/span><\/p>\n<ul>\n<li><span>V\u00a0<\/span><sub><span>1<\/span><\/sub><span>\u00a0= V\u00a0<\/span><sub><span>4<\/span><\/sub><span>\u00a0= V\u00a0<\/span><sub><span>max<\/span><\/sub><span>\u00a0= 500 \u00d7 10\u00a0<\/span><sup><span>-6<\/span><\/sup><span>\u00a0m\u00a0<\/span><sup><span>3<\/span><\/sup><span>\u00a0(0,5l)<\/span><\/li>\n<li><span>V\u00a0<\/span><sub><span>2<\/span><\/sub><span>\u00a0= V\u00a0<\/span><sub><span>3<\/span><\/sub><span>\u00a0= V\u00a0<\/span><sub><span>min<\/span><\/sub><span>\u00a0= V\u00a0<\/span><sub><span>m\u00e1x<\/span><\/sub><span>\u00a0\/ CR = 55,56 \u00d7 10\u00a0<\/span><sup><span>-6<\/span><\/sup><span>\u00a0m\u00a0<\/span><sup><span>3<\/span><\/sup><\/li>\n<\/ul>\n<p><span>Observe que (V\u00a0<\/span><sub><span>max<\/span><\/sub><span>\u00a0&#8211; V\u00a0<\/span><sub><span>min<\/span><\/sub><span>\u00a0) x n\u00famero de cilindros = cilindrada total do motor.<\/span><\/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><span>Exemplos de taxas de compress\u00e3o &#8211; Gasolina x Diesel<\/span><\/h2>\n<ul>\n<li><span>A taxa de compacta\u00e7\u00e3o em um motor a gasolina geralmente n\u00e3o ser\u00e1 muito maior que\u00a0<\/span><strong><span>10: 1<\/span><\/strong><span>\u00a0devido a uma poss\u00edvel batida no motor (autoigni\u00e7\u00e3o) e n\u00e3o menor que\u00a0<\/span><strong><span>6: 1<\/span><\/strong><span>\u00a0.<\/span><\/li>\n<li><span>Um Subaru Impreza WRX turbo tem uma taxa de compress\u00e3o de\u00a0<\/span><strong><span>8,0: 1<\/span><\/strong><span>\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.<\/span><\/li>\n<li><span>Um motor Honda S2000 (F22C1) tem uma taxa de compress\u00e3o de\u00a0<\/span><strong><span>11,1: 1<\/span><\/strong><span>\u00a0.<\/span><\/li>\n<li><span>Alguns motores de carros esportivos atmosf\u00e9ricos podem ter uma taxa de compress\u00e3o de at\u00e9\u00a0<\/span><strong><span>12,5: 1<\/span><\/strong><span>\u00a0(por exemplo, Ferrari 458 Italia).<\/span><\/li>\n<li><span>Em 2012, a Mazda lan\u00e7ou novos motores a gasolina sob a marca\u00a0<\/span><a href=\"https:\/\/en.wikipedia.org\/wiki\/SkyActiv\"><span>SkyActiv<\/span><\/a><span>\u00a0com uma\u00a0taxa de compress\u00e3o de\u00a0<\/span><strong><span>14: 1<\/span><\/strong><span>\u00a0.\u00a0Para reduzir o risco de bater no motor, o g\u00e1s residual \u00e9 reduzido usando\u00a0<\/span><a href=\"https:\/\/en.wikipedia.org\/wiki\/4-2-1_engine_exhaust_systems\"><span>sistemas de escape do motor 4-2-1<\/span><\/a><span>\u00a0, implementando uma cavidade do pist\u00e3o e otimizando a inje\u00e7\u00e3o de combust\u00edvel.<\/span><\/li>\n<li><span>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.<\/span><\/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><span>Efici\u00eancia t\u00e9rmica para o ciclo Otto<\/span><\/h2>\n<p><span>A\u00a0efici\u00eancia t\u00e9rmica do\u00a0<\/span><strong><span>ciclo Otto padr\u00e3o do ar<\/span><\/strong><span>\u00a0\u00e9 uma fun\u00e7\u00e3o da\u00a0<\/span><strong><span>taxa<\/span><\/strong><span>\u00a0de\u00a0<strong>compress\u00e3o<\/strong>\u00a0e\u00a0\u00a0<\/span><strong><span>\u03ba = c\u00a0<\/span><\/strong><strong><sub><span>p<\/span><\/sub><\/strong><strong><span>\u00a0\/ c\u00a0<\/span><\/strong><strong><sub><span>v<\/span><\/sub><\/strong><span>\u00a0.<\/span><\/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\"><span>Efici\u00eancia t\u00e9rmica para o ciclo Otto &#8211; \u03ba = 1,4<\/span><\/figcaption><\/figure>\n<p><span>\u00c9 uma conclus\u00e3o muito \u00fatil, porque \u00e9 desej\u00e1vel alcan\u00e7ar uma\u00a0<\/span><strong><span>alta taxa de compress\u00e3o<\/span><\/strong><span>\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<\/span><strong><span>reduz a temperatura do escapamento<\/span><\/strong><span>\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.<\/span><\/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><span>Autoigni\u00e7\u00e3o &#8211; Limite para taxa de compress\u00e3o<\/span><\/h2>\n<p><span>Em motores a gasolina comuns, a\u00a0<\/span><strong><span>taxa de compress\u00e3o<\/span><\/strong><span>\u00a0tem seus limites.\u00a0A taxa de compacta\u00e7\u00e3o em um motor a gasolina geralmente n\u00e3o ser\u00e1 muito maior que\u00a0<\/span><strong><span>10: 1<\/span><\/strong><span>\u00a0devido a uma poss\u00edvel\u00a0<\/span><strong><span>batida no<\/span><\/strong><span>\u00a0motor\u00a0(\u00a0<\/span><strong><span>autoigni\u00e7\u00e3o<\/span><\/strong><span>\u00a0) e n\u00e3o menor que\u00a0<\/span><strong><span>6: 1<\/span><\/strong><span>\u00a0.\u00a0Taxas de compress\u00e3o mais altas, no entanto, sujeitam os motores a gasolina a bater ao motor, causados \u200b\u200bpela\u00a0<\/span><strong><span>autoigni\u00e7\u00e3o de uma mistura n\u00e3o queimada<\/span><\/strong><span>\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<\/span><strong><span>batida do motor<\/span><\/strong><span>\u00a0pode ser reduzida usando\u00a0<\/span><strong><span>combust\u00edvel de alta octanagem<\/span><\/strong><span>, o que aumenta a\u00a0<\/span><strong><span>resist\u00eancia<\/span><\/strong><span>\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.<\/span><\/p>\n<p><span>Taxas de compress\u00e3o mais altas podem ser alcan\u00e7adas em\u00a0<\/span><strong><span>motores a diesel<\/span><\/strong><span>\u00a0(tamb\u00e9m chamados de\u00a0<\/span><strong><span>motores de igni\u00e7\u00e3o por compress\u00e3o<\/span><\/strong><span>\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.<\/span><\/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><span>Press\u00e3o Efetiva M\u00e9dia &#8211; MEP<\/span><\/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\"><span>O MEP \u00e9 uma medida muito \u00fatil da capacidade de um motor para executar um trabalho independente do deslocamento do motor.<\/span><\/figcaption><\/figure>\n<p><span>Um par\u00e2metro usado pelos engenheiros para descrever o desempenho dos motores de pist\u00e3o alternativo \u00e9 conhecido como\u00a0<\/span><strong><span>press\u00e3o efetiva m\u00e9dia<\/span><\/strong><span>\u00a0, ou\u00a0<\/span><strong><span>MEP<\/span><\/strong><span>\u00a0.\u00a0<\/span><strong><span>O MEP<\/span><\/strong><span>\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).<\/span><\/p>\n<p><span>Em geral, a\u00a0<\/span><strong><span>press\u00e3o efetiva m\u00e9dia<\/span><\/strong><span>\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:<\/span><\/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><span>Por exemplo, a\u00a0<\/span><strong><span>press\u00e3o efetiva m\u00e9dia<\/span><\/strong><span>\u00a0l\u00edquida\u00a0<strong>indicada<\/strong>\u00a0, conhecida como\u00a0<\/span><strong><span>IMEP\u00a0<\/span><sub><span>n<\/span><\/sub><\/strong><span>\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.<\/span><\/p>\n<p><span>Alguns exemplos:<\/span><\/p>\n<ul>\n<li><span>O MEP de um motor a gasolina atmosf\u00e9rico pode variar de 8 a 11 bar na regi\u00e3o de torque m\u00e1ximo.<\/span><\/li>\n<li><span>O MEP de um motor a gasolina turbo pode variar de 12 a 17 bar.<\/span><\/li>\n<li><span>O MEP de um motor diesel atmosf\u00e9rico pode variar de 7 a 9 bar.<\/span><\/li>\n<li><span>MEP de um motor diesel turboalimentado pode variar de 14 a 18 bar<\/span><\/li>\n<\/ul>\n<p><span>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<\/span><strong><span>caracter\u00edstica<\/span><\/strong><span>\u00a0\u00fatil\u00a0<strong>de um motor<\/strong>\u00a0.\u00a0Para dois motores de igual volume de cilindrada, aquele com um\u00a0<\/span><strong><span>MEP maior<\/span><\/strong><span>\u00a0produziria o\u00a0<\/span><strong><span>maior trabalho l\u00edquido<\/span><\/strong><span>\u00a0e, se os motores funcionassem na mesma velocidade,\u00a0<\/span><strong><span>maior pot\u00eancia<\/span><\/strong><span>\u00a0.<\/span><\/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><span>Ciclo Otto &#8211; Problema com solu\u00e7\u00e3o<\/span><\/h2>\n<p><span>Vamos assumir o\u00a0<\/span><a title=\"Ciclo Otto - Otto Engine\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-o-ciclo-otto-otto-engine-definicao\/\"><strong><span>ciclo Otto<\/span><\/strong><\/a><span>\u00a0, que \u00e9 um dos\u00a0<\/span><strong><span>ciclos termodin\u00e2micos<\/span><\/strong><span>\u00a0mais comuns\u00a0encontrados em\u00a0<\/span><strong><span>motores de autom\u00f3veis<\/span><\/strong><span>\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<\/span><em><span>V\u00a0<\/span><\/em><em><sub><span>1<\/span><\/sub><\/em><em><span>\u00a0\/ V\u00a0<\/span><\/em><em><sub><span>2<\/span><\/sub><\/em><span>\u00a0) \u00e9 conhecida como\u00a0<\/span><strong><span>taxa de compress\u00e3o<\/span><\/strong><span>\u00a0.<\/span><\/p>\n<p><span>A\u00a0<\/span><strong><span>taxa de compacta\u00e7\u00e3o<\/span><\/strong><span>\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).<\/span><\/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\"><span>diagrama pV do ciclo Otto.\u00a0A \u00e1rea delimitada pelo caminho completo do ciclo representa o trabalho total que pode ser realizado durante um ciclo.<\/span><\/figcaption><\/figure>\n<p><span>Neste exemplo, vamos assumir um ciclo Otto com\u00a0<\/span><strong><span>taxa<\/span><\/strong><span>\u00a0de\u00a0<strong>compress\u00e3o<\/strong>\u00a0de\u00a0<\/span><strong><span>CR = 9: 1<\/span><\/strong><span>\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<\/span><a title=\"Processo Adiab\u00e1tico\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-processo-adiabatico-definicao\/\"><span>expans\u00e3o adiab\u00e1tica<\/span><\/a><span>\u00a0\u00e9 T\u00a0<\/span><sub><span>4<\/span><\/sub><span>\u00a0= 800 K.<\/span><\/p>\n<ul>\n<li><span>Capacidade t\u00e9rmica espec\u00edfica a press\u00e3o constante do ar \u00e0 press\u00e3o atmosf\u00e9rica e \u00e0 temperatura ambiente:\u00a0<\/span><strong><span>c\u00a0<\/span><\/strong><strong><sub><span>p<\/span><\/sub><\/strong><strong><span>\u00a0= 1,01 kJ \/ kgK.<\/span><\/strong><\/li>\n<li><span>Capacidade t\u00e9rmica espec\u00edfica a um volume constante de ar \u00e0 press\u00e3o atmosf\u00e9rica e \u00e0 temperatura ambiente:\u00a0<\/span><strong><span>c\u00a0<\/span><\/strong><strong><sub><span>v<\/span><\/sub><\/strong><strong><span>\u00a0= 0,718 kJ \/ kgK.<\/span><\/strong><\/li>\n<li><strong><span>\u03ba = c\u00a0<\/span><\/strong><strong><sub><span>p<\/span><\/sub><\/strong><strong><span>\u00a0\/ c\u00a0<\/span><\/strong><strong><sub><span>v<\/span><\/sub><\/strong><strong><span>\u00a0= 1,4<\/span><\/strong><\/li>\n<\/ul>\n<p><strong><span>Calcular:<\/span><\/strong><\/p>\n<ol>\n<li><strong><span>a massa de entrada de ar<\/span><\/strong><\/li>\n<li><strong><span>a temperatura T\u00a0<\/span><\/strong><strong><sub><span>3<\/span><\/sub><\/strong><\/li>\n<li><strong><span>a press\u00e3o p\u00a0<\/span><\/strong><strong><sub><span>3<\/span><\/sub><\/strong><\/li>\n<li><strong><span>a quantidade de calor adicionada pela queima da mistura combust\u00edvel-ar<\/span><\/strong><\/li>\n<li><strong><span>a efici\u00eancia t\u00e9rmica deste ciclo<\/span><\/strong><\/li>\n<li><strong><span>o deputado<\/span><\/strong><\/li>\n<\/ol>\n<p><strong><span>Solu\u00e7\u00e3o:<\/span><\/strong><\/p>\n<p><span>1)\u00a0\u00a0<\/span><strong><span>a massa de entrada de ar<\/span><\/strong><\/p>\n<p><span>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:<\/span><\/p>\n<p><strong><em><span>pV = mR\u00a0<\/span><\/em><em><sub><span>espec\u00edfico<\/span><\/sub><\/em><em><span>\u00a0T<\/span><\/em><\/strong><\/p>\n<p><span>Onde:<\/span><\/p>\n<ul>\n<li><em><span>p<\/span><\/em><span>\u00a0\u00e9 a\u00a0<\/span><a title=\"Press\u00e3o absoluta\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/thermodynamic-properties\/what-is-pressure-physics\/absolute-pressure\/\"><span>press\u00e3o absoluta<\/span><\/a><span>\u00a0do g\u00e1s<\/span><\/li>\n<li><em><span>m<\/span><\/em><span>\u00a0\u00e9 a massa da subst\u00e2ncia<\/span><\/li>\n<li><em><span>T<\/span><\/em><span>\u00a0\u00e9 a\u00a0<\/span><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\/\"><span>temperatura absoluta<\/span><\/a><\/li>\n<li><em><span>V<\/span><\/em><span>\u00a0\u00e9 o volume<\/span><\/li>\n<li><em><span>R\u00a0<\/span><\/em><em><sub><span>espec\u00edfico<\/span><\/sub><\/em><span>\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<\/span><sub><span>espec\u00edfico<\/span><\/sub><span>\u00a0= 287,1 J.kg\u00a0<\/span><sup><span>-1<\/span><\/sup><span>\u00a0.K\u00a0<\/span><sup><span>-1<\/span><\/sup><span>\u00a0.<\/span><\/li>\n<\/ul>\n<p><span>Portanto<\/span><\/p>\n<p><strong><span>m<\/span><\/strong><span>\u00a0= p\u00a0<\/span><sub><span>1<\/span><\/sub><span>\u00a0V\u00a0<\/span><sub><span>1<\/span><\/sub><span>\u00a0\/ R\u00a0<\/span><sub><span>espec\u00edfico<\/span><\/sub><span>\u00a0T\u00a0<\/span><sub><span>1<\/span><\/sub><span>\u00a0= (100000 \u00d7 500 \u00d7 10\u00a0<\/span><sup><span>-6<\/span><\/sup><span>\u00a0) \/ (287,1 \u00d7 293) =\u00a0<\/span><strong><span>5,95 \u00d7 10\u00a0<\/span><\/strong><strong><sup><span>-4<\/span><\/sup><\/strong><strong><span>\u00a0kg<\/span><\/strong><\/p>\n<p><strong><span>Nesse problema, todos os volumes s\u00e3o conhecidos:<\/span><\/strong><\/p>\n<ul>\n<li><span>V\u00a0<\/span><sub><span>1<\/span><\/sub><span>\u00a0= V\u00a0<\/span><sub><span>4<\/span><\/sub><span>\u00a0= V\u00a0<\/span><sub><span>max\u00a0<\/span><\/sub><strong><span>=<\/span><\/strong><span>\u00a0500 \u00d7 10\u00a0<\/span><sup><span>-6<\/span><\/sup><span>\u00a0m\u00a0<\/span><sup><span>3<\/span><\/sup><span>\u00a0(0,5l)<\/span><\/li>\n<li><span>V\u00a0<\/span><sub><span>2<\/span><\/sub><span>\u00a0= V\u00a0<\/span><sub><span>3<\/span><\/sub><span>\u00a0= V\u00a0<\/span><sub><span>min<\/span><\/sub><span>\u00a0= V\u00a0<\/span><sub><span>m\u00e1x<\/span><\/sub><span>\u00a0\/ CR = 55,56 \u00d7 10\u00a0<\/span><sup><span>-6<\/span><\/sup><span>\u00a0m\u00a0<\/span><sup><span>3<\/span><\/sup><\/li>\n<\/ul>\n<p><span>Observe que (V\u00a0<\/span><sub><span>max<\/span><\/sub><span>\u00a0&#8211; V\u00a0<\/span><sub><span>min<\/span><\/sub><span>\u00a0) x n\u00famero de cilindros = cilindrada total do motor.<\/span><\/p>\n<p><span>2)\u00a0\u00a0<\/span><strong><span>a temperatura T\u00a0<\/span><\/strong><strong><sub><span>3<\/span><\/sub><\/strong><\/p>\n<p><span>Como o processo \u00e9 adiab\u00e1tico, podemos usar a seguinte rela\u00e7\u00e3o p, V, T para\u00a0<\/span><a title=\"Processo Adiab\u00e1tico\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-processo-adiabatico-definicao\/\"><span>processos adiab\u00e1ticos<\/span><\/a><span>\u00a0:<\/span><\/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><span>portanto<\/span><\/p>\n<p><strong><span>T\u00a0<\/span><sub><span>3<\/span><\/sub><\/strong><span>\u00a0= T\u00a0<\/span><sub><span>4<\/span><\/sub><span>\u00a0.\u00a0CR\u00a0<\/span><sup><span>k &#8211; 1<\/span><\/sup><span>\u00a0= 800.\u00a09\u00a0<\/span><sup><span>0,4<\/span><\/sup><span>\u00a0=\u00a0<\/span><strong><span>1926 K<\/span><\/strong><\/p>\n<p><span>3)\u00a0\u00a0<\/span><strong><span>a press\u00e3o p\u00a0<\/span><\/strong><strong><sub><span>3<\/span><\/sub><\/strong><\/p>\n<p><span>Novamente, podemos usar a\u00a0<\/span><a title=\"Lei do g\u00e1s ideal\" href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/thermodynamics\/ideal-gas-law\/\"><span>lei do g\u00e1s ideal<\/span><\/a><span>\u00a0para encontrar a press\u00e3o no in\u00edcio do curso de for\u00e7a como:<\/span><\/p>\n<p><strong><span>p\u00a0<\/span><\/strong><strong><sub><span>3<\/span><\/sub><\/strong><span>\u00a0= mR\u00a0<\/span><sub><span>espec\u00edfico<\/span><\/sub><span>\u00a0T\u00a0<\/span><sub><span>3<\/span><\/sub><span>\u00a0\/ V\u00a0<\/span><sub><span>3<\/span><\/sub><span>\u00a0= 5,95 \u00d7 10\u00a0<\/span><sup><span>-4<\/span><\/sup><span>\u00a0x 287,1 x 1926 \/ 55,56 \u00d7 10\u00a0<\/span><sup><span>-6<\/span><\/sup><span>\u00a0= 5920000 Pa =\u00a0<\/span><strong><span>59,2 bar<\/span><\/strong><\/p>\n<p><span>4)\u00a0\u00a0<\/span><strong><span>a quantidade de calor adicionada<\/span><\/strong><\/p>\n<p><span>Para calcular a quantidade de calor adicionada pela queima da mistura combust\u00edvel-ar,\u00a0<\/span><sub><span>adicione<\/span><\/sub><span>\u00a0Q\u00a0, temos que usar a\u00a0<\/span><a title=\"Primeira Lei da Termodin\u00e2mica\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-a-primeira-lei-da-termodinamica-definicao\/\"><span>primeira lei da termodin\u00e2mica<\/span><\/a><span>\u00a0para\u00a0<\/span><a title=\"Processo Isoc\u00f3rico - Processo Isom\u00e9trico\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-o-processo-isocorico-processo-isometrico-definicao\/\"><span>processos isoc\u00f3ricos<\/span><\/a><span>\u00a0, que declara Q\u00a0<\/span><sub><span>add<\/span><\/sub><span>\u00a0= \u2206U, portanto:<\/span><\/p>\n<p><strong><span>Q\u00a0<\/span><sub><span>add<\/span><\/sub><span>\u00a0= mc\u00a0<\/span><sub><span>v<\/span><\/sub><span>\u00a0(T\u00a0<\/span><sub><span>3<\/span><\/sub><span>\u00a0&#8211; T\u00a0<\/span><sub><span>2<\/span><\/sub><span>\u00a0)<\/span><\/strong><\/p>\n<p><span>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<\/span><strong><span>1 \u2192 2.<\/span><\/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><span>T\u00a0<\/span><sub><span>2<\/span><\/sub><\/strong><span>\u00a0= T\u00a0<\/span><sub><span>1<\/span><\/sub><span>\u00a0.\u00a0CR\u00a0<\/span><sup><span>k &#8211; 1<\/span><\/sup><span>\u00a0= 293.\u00a09\u00a0<\/span><sup><span>0,4<\/span><\/sup><span>\u00a0=\u00a0<\/span><strong><span>706 K<\/span><\/strong><\/p>\n<p><span>ent\u00e3o<\/span><\/p>\n<p><strong><span>Q\u00a0<\/span><\/strong><strong><sub><span>add<\/span><\/sub><\/strong><span>\u00a0= mc\u00a0<\/span><sub><span>v<\/span><\/sub><span>\u00a0(T\u00a0<\/span><sub><span>3<\/span><\/sub><span>\u00a0&#8211; T\u00a0<\/span><sub><span>2<\/span><\/sub><span>\u00a0) = 5,95 \u00d7 10\u00a0<\/span><sup><span>-4<\/span><\/sup><span>\u00a0x 718 x 1220 =\u00a0<\/span><strong><span>521,2 J<\/span><\/strong><\/p>\n<p><span>5)\u00a0\u00a0<\/span><strong><span>a efici\u00eancia t\u00e9rmica<\/span><\/strong><\/p>\n<p><a title=\"Efici\u00eancia t\u00e9rmica\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-eficiencia-termica-definicao\/\"><strong><span>Efici\u00eancia t\u00e9rmica<\/span><\/strong><\/a><span>\u00a0para um ciclo Otto:<\/span><\/p>\n<p><span>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:<\/span><\/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><span>6)\u00a0\u00a0<\/span><strong><span>a press\u00e3o efetiva m\u00e9dia<\/span><\/strong><\/p>\n<p><span>O\u00a0<\/span><strong><span>MEP<\/span><\/strong><span>\u00a0foi definido como:<\/span><\/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><span>Nesta equa\u00e7\u00e3o, o volume de deslocamento \u00e9 igual a V\u00a0<\/span><sub><span>max<\/span><\/sub><span>\u00a0&#8211; V\u00a0<\/span><sub><span>min<\/span><\/sub><span>\u00a0.\u00a0O trabalho l\u00edquido para um ciclo pode ser calculado usando o calor adicionado e a efici\u00eancia t\u00e9rmica:<\/span><\/p>\n<p><strong><em><span>W\u00a0<\/span><\/em><\/strong><strong><em><sub><span>net<\/span><\/sub><\/em><\/strong><em><span>\u00a0=\u00a0<\/span><\/em><em><span>Q\u00a0<\/span><\/em><em><sub><span>add<\/span><\/sub><\/em><em><span>\u00a0.\u00a0\u03b7\u00a0<\/span><\/em><em><sub><span>Otto<\/span><\/sub><\/em><em><span>\u00a0=\u00a0<\/span><\/em><em><span>521,2 x 0,5847 = 304,7\u00a0<\/span><strong><span>J<\/span><\/strong><\/em><br \/>\n<strong><em><span>MEP<\/span><\/em><\/strong><em><span>\u00a0= 304,7 \/ (<\/span><\/em><span>\u00a0500 \u00d7 10<\/span><sup><span>\u00a0-6<\/span><\/sup><span>\u00a0&#8211; 55,56 \u00d7 10<\/span><sup><span>\u00a0-6\u00a0<\/span><\/sup><em><span>) = 685,6 kPa =\u00a0<\/span><strong><span>6,856 bar<\/span><\/strong><\/em><\/p>\n<\/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>Motor a gasolina a quatro tempos &#8211; Otto Cycle.\u00a0Como funciona o motor a quatro tempos.\u00a0Um curso refere-se ao curso completo do pist\u00e3o ao longo do cilindro, em qualquer dire\u00e7\u00e3o.\u00a0Engenharia T\u00e9rmica Ciclo Otto &#8211; Otto Engine Em 1876, um engenheiro alem\u00e3o,\u00a0Nikolaus August Otto,\u00a0avan\u00e7ou no estudo de motores t\u00e9rmicos construindo o primeiro motor de quatro tempos em &#8230; <a title=\"O que \u00e9 o motor a gasolina a quatro tempos &#8211; Otto Cycle &#8211; Defini\u00e7\u00e3o\" class=\"read-more\" href=\"https:\/\/www.thermal-engineering.org\/pt-br\/o-que-e-o-motor-a-gasolina-a-quatro-tempos-otto-cycle-definicao\/\" aria-label=\"More on O que \u00e9 o motor a gasolina a quatro tempos &#8211; Otto Cycle &#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 motor a gasolina a quatro tempos - Otto Cycle - Defini\u00e7\u00e3o<\/title>\n<meta name=\"description\" content=\"Motor a gasolina a quatro tempos - Otto Cycle. 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