Research On The Effects Of In-cylinder Steam Injection On Thermodynamic Cycle And Combustion Of The Gas Engine

The development of efficient and clean internal combustion engine?ICE?technology is the core of the ICE research at present.In the intake manifold steam injection?IMSI?method,exhaust is employed to heat water to produce steam,which is injected into the intake pipe to reduce engine emissions by changing in-cylinder combustion.In this thesis,for the poor engine power and fuel economy caused by IMSI,in-cylinder steam injection?ICSI?is proposed to comprehensively improve engine performance and reduce emissions.The main research contents of the paper include:1.An IMSI gas engine platform is established and used to investigate the relationships between IMSI and power,brake specific fuel consumption?BSFC?and emissions.It is found that,since the decrease of volumetric efficiency and the prolonged afterburning period,IMSI leads to the reduction of engine power and the increase of BSFC.2.ICSI is proposed.And according to steam injection stage,ICSI is divided into compression stroke in-cylinder steam injection?CSICSI?and power stroke in-cylinder steam injection?PSICSI?.The influences of ICSI on the working cycle of the gas engine and the heat exchange process between water and exhaust are analyzed by thermodynamics.A combined cycle of mixed working medium based on in-cylinder steam injection of ICE is proposed.A thermodynamic model of the gas engine is used to research the characteristics of the combined cycle.The limits of ICSI mass,temperature and timing are studied.Besides,the effects of those ICSI parameters on engine power and brake specific fuel consumption?BSFC?are further investigated.It is found that ICSI mass and timing are the key parameters which affect engine performance significantly.However,ICSI mass is limited by the minimum temperature difference at the pinch point of the heat exchanger and the exhaust temperature at the outlet of evaporator.Besides,ICSI timing is limited by in-cylinder pressure.ICSI temperature has little effect on engine power and BSFC.But,it is limited by ICSI pressure.3.Expect changing engine thermodynamic cycle,for CSICSI,the influence of steam on gas combustion characteristics is another important reason which impacts the engine performance and emissions characteristics.Based on the detailed chemical kinetic mechanism of gas?including CH₄ and C₃H₈?,the laminar premixed flame model of gas is established.By the model,the influences of steam on the laminar flame propagation speed and the formation of pollutants are analyzed.Since without considering the non-linear effect of steam on the dilution term,the fuel laminar flame propagation velocity model cannot accurately predict the gas laminar flame propagation velocity under steam dilution.Based on experimental data,by modifying temperature index and pressure index and introducing dilution term index,a gas laminar flame propagation velocity model suitable for steam dilution is established.4.Based on quasi-dimensional combustion and emission model and computational fluid dynamics?CFD?model of the gas engine,the influences of CSICSI and CSICSI coupling ignition advance angle on the in-cylinder combustion and engine performance are researched.It is found that,for the decrease of gas laminar flame propagation velocity,CSICSI prolongs the main combustion period.However,ignition advance angle can effectively adjust the engine combustion phase with CSICSI.According to the characteristics of the effects of ignition advance angle,CSICSI and PSICSI on the gas engine performance and emissions,a strategy of ignition advance angle coupling two-stage ICSI is proposed to further improve engine performance and reduce emissions.The simulation results show that under full-load characteristics,the maximum increase of engine torque is up to 9.3%,the maximum reduction of BSFC is up to 8.7%,and the maximum decreases of NO,CO and HC are 85.3%,57.3%and 92.6%,respectively.5.Based on the IMSI gas engine platform,an equivalent CSICSI experimental method is used to verify the effectiveness of CSICI and CSICSI coupling ignition advance angle to improve engine performance and reduce emissions.The experimental results show that under the equivalent CSICSI condition,the maximum increase of engine power is 3.7%,the maximum reduction of BSFC is 3.9%,the maximum decrease of NO is 90.3%,CO is less than 0.02%,and HC is less than 60ppm.Besides,under the equivalent CSICSI coupling ignition advance angle condition,the maximum increase of engine power is up to 10.9%,the maximum decrease of BSFC is 4.0%,the maximum reduction of NO is 82.0%,CO is less than 0.01%,and HC is less than 35ppm.