采用非同步进气正时和增压器匹配提升天然气发动机的低速性能

Low-Speed Performance Improvement of Natural Gas Engine by Asynchronous Intake Timing and Turbocharger Matching

为了提升由增压汽油机改造的天然气发动机的低速性能,设计了同步进气和非同步进气结合增压器匹配的优化方案,并通过台架试验和数值模拟的方法研究了各方案对天然气发动机性能的影响。天然气发动机匹配比原汽油机小的增压器显著提高了低速时的增压比,进而增加了进气流量。采用比原汽油机进气持续角和进气迟闭角小的同步进气方案,减小了发动机低速时的进气末期回流,使得低速时进气流量显著增加;在此基础上,采用非同步进气方案,其中一个进气门的进气持续角进一步减小,导致低速时进气流量进一步增加,相对原机方案进气流量最大增加了46%,而另一个进气门进气持续角和进气迟闭角较大,保证了高速时可充分进气。采用非同步进气方案时缸内流动状况得到改善,最大燃烧放热率显著增加,燃烧持续期略有缩短。天然气发动机的性能经过优化后,相比原汽油机,低速扭矩最大提高了55.6%,经济性也有所改善,低速燃气消耗率最大降低了8.1%。

Optimization schemes of synchronous and asynchronous intake timing combined with turbocharger matching are designed to improve the low-speed performance of a natural gas engine modified from a turbocharged gasoline engine. Then bench test and numerical simulation are used to investigate the effects of different intake optimization schemes on the performance of the natural gas engine. It is found that the boost pressure and the intake flow rate of the natural gas engine at low speeds increase obviously by matching a turbocharger smaller than that of the original gasoline engine. The backflow at the end of intake stroke is reduced at low speeds when adopting the synchronous intake timing scheme with a smaller intake duration angle and delayed closing angle, which results in an obvious increase in the intake flow rate at low speeds. When adopting asynchronous intake timing scheme, the further decreased intake duration angle of one intake valve may lead to a further increase of 46% in the intake flow rate at low speeds compared with the original scheme;the other intake valve with larger intake duration angle and delayed closing angle ensures sufficient intake flow rate at high speeds. At the same time, the asynchronous intake timing scheme can improve the in-cylinder flow, increase the maximum heat release rate, and slightly shorten the combustion duration. After the optimization of the turbocharged natural gas engine, the low-speed torque is increased by 55.6%, which exceeds that of the original gasoline engine. The low-speed fuel economy is also improved, and the brake specific gas consumption is reduced by 8.1%.