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Influence of Piston Crown Geometry for Compressed Natural Gas SI Engines: Performance Evaluation and Emissions

机译：活塞冠几何对压缩天然气SI发动机的影响：性能评估和排放

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Alternative transportation fuels have been receiving increasing attention as likely solutions to the problems of urban air quality, global warming and strategically important excessive dependence on imported oil. Natural gas as a motor fuel, has advantages such as a very good ability for easy mixture formation, both outside and inside the engine cylinder, a wide range of air-fuel ratios (leading to lean or extremely lean mixtures), high heating value and antiknock resistance. These properties enable this SI engine to work with relative high compression ratios and therefore a higher total efficiency. Exhaust emissions are directly related to the fuel consumption by vehicles, which in turn, are related to the number of vehicles. The fuel consumption by transportation sector in Delhi city was estimated to be about 250,000 tonnes of petrol and about 50,000 tonnes of high speed diesel in the year 1989 by the Central Pollution Control Board and the trend is rising exponentially with the increase in number of vehicles and the present date is witnessing a steep rise in the number of usage of alternately fueled vehicles to curtail emissions. The performances of alternate fueled engines are low compared to the base engines with a major thrust given to retrofit systems. Dedicated engines desire major design changes to complete the conventional fuels and in the attempt to develop a dedicated compressed natural gas engine technology, the initial attempt was to experimentally evaluate the significance of the piston crown geometry on an existing OEM engine to optimize the crown geometry. Three piston geometries were identified and experimented on a 100 cc single cylinder 4-Stroke SI engine. The performance curves were compared at different load conditions under both gasoline and compressed natural gas (CNG) mode and the optimal piston was evaluated. The results show a remarkable change in power and performance aspects due to the change in the piston crown geometries. The engine when run in CNG mode was able to deliver adequate power to compete the conventional gasoline engines. The engine under the gasoline mode ran close to stoichiometric conditions whereas in CNG mode the engine ran extremely lean.
机译：替代交通燃料一直受到城市空气质量问题，全球变暖和战略性重要的依赖性的可能性越来越多的关注。天然气作为电机燃料，具有非常好的能力，例如易于混合形成，在发动机缸外部和内部，宽范围的空气燃料比（导致瘦或极其瘦的混合物），加热值高抗抗震性。这些属性使得该Si引擎能够与相对高压缩比合作，因此效率更高。废气排放与车辆的燃料消耗直接相关，这又与车辆数量有关。德里市运输部门的燃料消耗估计，1989年，中央污染管制委员会的汽油约25万吨，大约5万吨高速柴油，趋势随着车辆数量的增加而呈指数级增长目前的日期目睹了交替燃料车辆的使用数量急剧上升以减少排放。与具有给予改装系统的主要推力的基本发动机相比，替代燃料发动机的性能低。专用发动机渴望重大设计改变以完成传统燃料，并试图开发专用压缩的天然气发动机技术，初步尝试是通过实验评估活塞冠几何形状在现有OEM发动机上的意义，以优化冠状几何形状。鉴定了三个活塞几何形状，并在100CC单缸4行程Si发动机上进行实验。在汽油和压缩天然气（CNG）模式下的不同载荷条件下比较了性能曲线，评价最佳活塞。由于活塞冠状几何形状的变化，结果表明功率和性能方面的显着变化。在CNG模式下运行时发动机能够提供足够的功率来竞争传统的汽油发动机。汽油模式下的发动机沿着化学计量的条件跑到，而在CNG模式下，发动机耗尽极端倾斜。

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