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首页> 外文会议>ASME(American Society of Mechanical Engineers) Internal Combustion Engine Division Fall Technical Conference; 20071014-17; Charleston,SC(US) >THE EFFECTS OF COMPRESSION RATIO AND EXPANSION RATIO ON ENGINE PERFORMANCE INCLUDING THE SECOND LAW OF THERMODYNAMICS: RESULTS FROM A CYCLE SIMULATION
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THE EFFECTS OF COMPRESSION RATIO AND EXPANSION RATIO ON ENGINE PERFORMANCE INCLUDING THE SECOND LAW OF THERMODYNAMICS: RESULTS FROM A CYCLE SIMULATION

机译：压缩比和膨胀比对包括热力学第二定律在内的发动机性能的影响：循环模拟的结果

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摘要

This investigation quantified the effects of compression ratio and expansion ratio on performance, efficiency, and second law parameters for an automotive, spark-ignition engine. The well known increase in engine performance for increasing compression ratio and expansion ratio is demonstrated. These increases for brake engine performance are modest for compression ratios greater than about 10 for the conditions studied. The results demonstrated that the increasing friction and heat losses for the higher compression ratios are of the same order as the thermodynamic gains. Also, the results included the destruction of availability during combustion. For a part load condition, the availability destroyed decreased from about 23% for a compression ratio of 4 to about 21% for a compression ratio of 10. In addition, this study examined cases with greater expansion ratios than compression ratios. The overall cycle for these cases is often called an "Atkinson" cycle. For most cases, the thermal efficiency first increased as expansion ratio increased, attained a maximum efficiency, and then decreased. The decrease in efficiency after the maximum value was due to increased heat losses, increased friction, and ineffective exhaust processes (due to the reduced cylinder pressure at the time of exhaust valve opening). For part load cases, the higher expansion ratio provided only modest gains due to increased pumping losses associated with the constant load requirement. For the wide open throttle cases, however, the higher expansion ratios provided significant gains. For example, for a compression ratio of 10, expansion ratios of 10 and 30 provided brake thermal efficiencies of about 34% and 43%, respectively. Although the net thermodynamic gains are significant, large expansion ratios such as 30 may not be practical in most applications.
机译：这项研究量化了压缩比和膨胀比对汽车火花点火发动机的性能，效率和第二定律参数的影响。已经证明了众所周知的增加压缩比和膨胀比的发动机性能的提高。对于所研究的条件，对于大于约10的压缩比，制动发动机性能的这些增加是适度的。结果表明，较高的压缩比下增加的摩擦和热损失与热力学增益相同。同样，结果包括燃烧过程中可用性的破坏。对于部分负载情况，可用率从压缩比4的约23％降低到压缩比10的约21％。此外，本研究研究了膨胀比大于压缩比的情况。这些情况的整个周期通常称为“阿特金森”周期。在大多数情况下，热效率首先随着膨胀比的增加而增加，达到最大效率，然后下降。最大值之后效率降低是由于热量损失增加，摩擦增加以及排气过程无效（由于排气门打开时气缸压力降低）。对于部分负载情况，由于与恒定负载要求相关的泵送损耗增加，因此较高的膨胀率仅提供了适度的增益。但是，对于节气门全开的情况，较高的膨胀比提供了可观的收益。例如，对于10的压缩比，10和30的膨胀比分别提供了大约34％和43％的制动热效率。尽管净热力学增益显着，但是在大多数应用中，较大的膨胀比（例如30）可能并不实际。

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