Experimental Study Of Medium-duty Gasoline Engine Combustion Optimization Based On Equivalent Combustion

With the rapid development of the road transportation industry,the development of efficient and clean medium-duty commercial vehicle engines has become an urgent need at present.The development of equivalent combustion gasoline engine based on diesel engine platform has the characteristics of low cost and soft working,which can better adapt to the requirements of medium-duty commercial vehicles under urban operating conditions,and the high body strength of diesel engine also provides favorable conditions for thermal efficiency improvement.However,for the mediumduty gasoline engine based on diesel platform,its combustion system structure and operating characteristics make the problem of knocking more prominent,which is a key factor limiting the improvement of thermal efficiency.Therefore,there is a need to find ways and strategies to effectively suppress the knocking and improve the thermal efficiency.Based on this,this paper will focus on the combustion system,fuel characteristics,combustion control and so on to carry out equivalent combustion optimization research of medium-duty gasoline engine,so as to provide reference for the development of efficient combustion technology of medium-duty gasoline engine.Firstly,the effects of late intake valve closing,intake port and combustion chamber structure on the in-cylinder combustion and thermal efficiency of a mediumduty gasoline engine based on a diesel engine conversion trial were investigated.The results show that the late intake valve closing scheme can effectively suppress the knocking,advance the ignition time and combustion phase,shorten the combustion duration and reduce the pumping loss,and combined with EGR optimization can further improve the thermal efficiency,but at higher EGR rate,the thermal efficiency improvement will be limited by the reduced combustion rate.The compound intake port can effectively improve the combustion phase and increase the EGR tolerance compared with the original double-spiral intake port,while the inverted wedge-shaped combustion chamber has different degrees of improvement in combustion duration or combustion phase under different loads,which can achieve thermal efficiency improvement in a wide load range.The use of late intake valve closing,compound intake port and inverted wedge combustion chamber combined with combustion control optimization can improve the maximum indicated thermal efficiency by 4.92%relative to the original no-EGR baseline.The effect of ethanol blending ratio on the combustion and thermal efficiency of a medium-duty gasoline engine was further investigated based on the combustion system optimization scheme of late intake valve closing,compound intake port matched with inverted wedge-shaped combustion chamber.The results show that increasing the blending ratio of ethanol to 20% can effectively suppress the knocking,advance the optimal ignition time,optimize the combustion phase,and improve the indicated thermal efficiency.E20 fuel combined with EGR and combustion control optimization achieves the highest indicated thermal efficiency of 44.08% at 2000r/min,0.63 MPa BMEP working condition.Compared to commercially available ethanol gasoline E10,the improvement is 0.71%,while the improvement in thermal efficiency is 5.63% compared to the original engine without EGR.