Effect Of EGR Stratification On Performance Of Natural Gas Engine

All the time, energy and environment have been the most important two big issues thathuman faces, how to further improve the utilization percent of the fuel to reduce emissionsof internal combustion engine, to meet the increasing stringent emissions regulationsbecome the focus of the research. In recent years, the development of efficient and cleanengine industry has become more and more popular. Natural gas, which has thecharacteristics of large reserves, cheaper than the oil, lower carbon emissions and friendly tothe environment, has become more and more favored by the majority of automobilemanufacturers. But at present, natural gas engine cannot meet the increasingly stringentemission regulations, because of the engine having a large cyclical variation, a low thermalefficiency and the emission deterioration problem in some working conditions. EGR hasbeen proved to be an effective method to reduce NO_xemission by a large number ofpractices.The natural gas engine that research uses is remaked through a diesel engine. Startingfrom the aspect of EGR internal cylinder stratification, we developed an inflow stratifiedinjection device and received a national patent. The name of this patent is: Natural gasengine inflow stratified injection device, and the NO. is201210087211.4. This device’sfeatures include: a. Wrapped in stratifications of spray air, EGR and CNG; b. EGR andCNG gas mixture with air stratificationing wrapped injection; c. the gas, mixed by EGR andair, stratified injection with CNG. This device doesn’t make EGR mix with the air but wrapsaround the gas and mixed with the gas in air inlet and get into the cylinder together. Hence,the device is beneficial to the gas entered into the cylinder, air, EGR stratificationcombustion, increasing the feasibility of reducing emissions and improving the economiclimit. It also provides a new solution to reduce the emission of NO_x, while maintaining ahigh thermal efficiency. Based on the combustion boundary parameter optimization, theexperimental analysis device introduces EGR influencing regular pattern on combustionprocess and emissions of lean-burn natural gas engine. The introduction of EGR has morepractical engineering significance than others that mixed inert gas. This study selected1450r/min25%and1750r/min25%working condition, thespecific study results are as follows:Based on opening degree of EGR:1With the increasing of EGR opening degree, the amount of exhaust gas that enteredinto the cylinder increased in each cycle, the peak heat release rate decreased, NO_xemissions showed a linear downward trend and up to80%at most; when the EGR valveopened more than10%, the engine output torque and fuel economy began to decline, andwhen the EGR valve opening degree is increased to15%, the engine output torque decreaseof more than5%.2Under the same conditions, keeping other combustion parameters unchanged, withthe increasing opening scale of throttle valve, the engine output torque was increased at firstand then decreased, the gas consumption ratio was first decreased and then increased, theNO_x emissions decreased, the HC emissions increased slightly.3Under the same conditions, keeping other combustion parameters unchanged, withthe ignition timing or injection moment moving up, the output torque was slightlyincreasing, the gas consumption ratio was first decreasing and then increased, the NO_xemissions increased.