Numerical Simulation Of The Homogeneous Charge Compression Ignition Of Ethanol With Internal EGR

As the fast development of the national economy and the number of the automobile increasing, the question of oil shortage prominents day by day, the automobile emissions are polluting the atmospheric environment seriously day by day. Therefore it is important to enhance the efficiency of automobile energy and reduce the noxious emmissions, which can not only save the oil resource but also protect the atmospheric environment .As a result of the nature difference of gasoline and the diesel fuel, the traditional internal combustion engine divides into the spark ignition engine (gasoline engine) and compress ignition engine (diesel engine). Diesel engine belongs to atomization proliferation combustion. Because the formation time of the mixture is short, the non-uniformity forms the partial high temperature flame area and the high temperature excessively thick area.It is extremely easy to form NOx and the carbon smoke. But it has high compression ratio and high thermal efficiency . The traditional gasoline engine belongs to the isotropic mixture, flame-propagation combustion.It gets to light with the aid of the igniter plug. As a result of the engine knock limit, it only can use a lower compression ratio, and use the damper to control load. Therefore the efficiency of the fuel is lower than the diesel engine approximately 30%. Also it produces massive NOx and the incomplete combustion products. But there are no carbon smoke discharges.But in recently several years, Homogeneous Charge Compression Ignition (HCCI) synthesized the merit of the traditional gasoline engine and the diesel engine。It not only is equal to the diesel engine thermal efficiency but also has no carbon smoke discharge and there is extremely low NOx to discharge.So it has attracted widespread attention of the internal combustion engine field. But HCCI combustion of the high octane value fuel actually faces the fire difficulty and the difficult of combustion rate control. The earlier period research indicated that theuses of internal EGR solves these two questions effectively.1. This article has established the ethyl alcohol HCCI engine circulation model coupling unidimensional cycles of engine simulation software GT-Power and the large-scale chemical kinetics analysis software CHEMKIN2. The effect of fully flexible valve actuation system driven by the camless electro-hydraulic valve operating system is analyzed to find the effect of the different match factor to the in internal EGR rate and the compression initial period in-cylinder temperature.Simulated match plans includes: Change exhaust valve close timing, change exhaust valve open timing, change intake valve to open timing and change the exhaust valve lift. The results indicates : In the case of the maintenance of the exhaust valve open timing and intake valve close timing,changing the exhaust valve close timing can gain 56.2% internal EGR. In order to enhance internal EGR rate,it is possible to retard the intake valve open timing , retard exhaust valve open timing or reduce exhaust valve lift. All these method may enhance the internal EGR rate, and enable it to achieve 80%. Simultaneously the influence to the initial temperature of the different EGR rate is analyzed.3. Using this circulation model studis the influence of internal EGR rate to the ethyl alcohol HCCI combustion process.The results indicates that:(1) when EGR rate is smaller than 40%, cylinder internal pressure elevating rate is bigger than 0.6MPa/°CA .this can bring the knock. Therefore the ethyl alcohol HCCI load upper limit is equal to 40% definited by EGR rate. When EGR rate is bigger than 80%, it appears misfire. Therefore the ethyl alcohol fuel HCCI load lower limit is equal to 80% definited by EGR rate.(2) The internal EGR has the dual function to the HCCI , one function is to heat fresh air to make it easy to fire;the other function is the heat capacity and the dilution function,which may reduce the chemical reaction speed , postpone the fire, lengthen the burning duration and depressurize elevating rate. When EGR rate is smaller than 55% heat function performance to be remarkable. Along with EGRrate increasing, fire beginning spot is ahead of time; When EGR rate is bigger than55%, reducing the chemical reaction rate act to be remarkable role. Along with the EGR rate increasing, the fire beginning spot postpones.(3) This model is used to forecast the range of the speed and the load of theHCCI engine.