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首页> 外文期刊>Applied Energy >Investigations on the effects of fuel stratification on auto-ignition and combustion process of an ethanol/diesel dual-fuel engine
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Investigations on the effects of fuel stratification on auto-ignition and combustion process of an ethanol/diesel dual-fuel engine

机译：燃料分层对乙醇/柴油双燃料发动机自燃和燃烧过程的影响研究

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In dual-fuel engines, the fuel stratification produced by direct in-cylinder blending of port injected and direct injected fuels is important for combustion and emission control, while the fuel stratification could be influenced by port fuel proportion, direct injection strategy as well as geometry of direct injector. In this paper, based on an ethanol/diesel dual-fuel engine, experiments and simulations have been conducted to study how these factors influence in-cylinder fuel stratification as well as auto-ignition and combustion process. The equivalence ratio of premixed ethanol, maximum local equivalence ratio and fuel concentration gradients in radial and circumferential directions of the cylinder were used to evaluate the fuel stratification. Under the tested dual-fuel conditions, the results showed that auto-ignition was more likely to first occur in regions with mixture near stoichiometric ratio, rather than regions with mixtures exhibiting highest fuel reactivity. As a consequence, larger equivalence ratio of premixed ethanol could prolong ignition delay of in-cylinder charge by reducing the fuel reactivity of regions where ignition kernels first occurred. Meanwhile, as the fuel rich regions produced by retarded diesel injection could not further extend the ignition delay gradient, the improved fuel reactivity and higher local equivalence ratio consequently resulted in steeper heat release rate. Additionally, the experimental results showed that with reduced nozzle holes, the peak pressure and heat release rate of dual-fuel operation could be decreased. This is mainly because fewer nozzle holes could result in fuel stratification in both circumferential and radial directions, thus the development of combustion zone was slowed down and consequently the heat release rate was decreased.
机译：在双燃料发动机中，进气道喷射和直接喷射的缸内直接缸内混合产生的燃料分层对于燃烧和排放控制很重要，而燃料分层可能会受到进气道燃料比例，直接喷射策略以及几何形状的影响直接喷油器。在本文中，基于乙醇/柴油双燃料发动机，已经进行了实验和模拟，以研究这些因素如何影响缸内燃料分层以及自燃和燃烧过程。使用预混乙醇的当量比，最大局部当量比和气缸径向和圆周方向上的燃料浓度梯度来评估燃料分层。在测试的双燃料条件下，结果表明，自燃更容易发生在具有接近化学计量比的区域，而不是具有最高燃料反应性的区域。结果，较大的预混乙醇当量比可以通过降低首次出现点火核的区域的燃料反应性来延长缸内装料的点火延迟。同时，由于通过延迟柴油喷射产生的燃料富集区域不能进一步扩展点火延迟梯度，因此改善的燃料反应性和更高的局部当量比导致了更陡的放热率。另外，实验结果表明，通过减少喷嘴孔，可以降低双燃料运行的峰值压力和放热率。这主要是因为较少的喷嘴孔可导致燃料在周向和径向上分层，从而使燃烧区的发展变慢，因此放热率降低。

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