Impact Of Dilution Gas And Entrance Mode On The Performance Of A Natural Gas Engine

Natural gas which is an alternative fuel for petrol and diesel fossil fuels is extensivelyapplied for its rich resources and clean emissions. In order to guarantee the high fuel economyof test engine and reduce NOx emissions in natural gas engine, this experiment is conductedunder equivalence ratio and lean burn conditions with different dilution gases and modes toresearch the effects on the performance of combustion and emissions.The mature EGR technique applied in petrol and diesel engine can be also applied innatural gas engine. Meanwhile with the usage of lean burn technology, the brake specific fuelconsumption（be）and NOx emissions can be both reduced. Although EGR is able to restrainNOx emissions, fuel economy is affected under high EGR ratio. The control accuracy of EGRand the intake pressure between intake air and EGR are the main obstacles in using in naturalgas engine. A new injection device is applied in this work and the influence of different dilutiongases with various dilution ratios (DR) and dilution modes on natural gas engine are researched.This experiment is conducted on a six cylinders, multi-point injection, electronic controland turbocharged natural gas engine under1450r/min,50%load operating condition. Thedilution gases used in this experiment are CO2, N2and Ar. The range of DR is0-135%andintroduction modes are inside-outside tube and inside tube. Research results are as follows:NOx emissions are reduced with increasing DR and excess air coefficient (λ) under threedilution gases. Mixing CO2has the most obvious effect on reducing NOx emissions at the sameDR. The largest drop of NOx emissions when mixing CO2at equivalence ratio is52.6%. NOxemissions are respectively reduced by36.4%and35.9%when mixing CO2and N2under1.4excess air coefficient. The effect of mixing Ar is not obvious in reducing NOx emissions buthigh fuel economy can be acquired. For example, mixing Ar by135%DR at1.2excess aircoefficient is able to reduce fuel economy by1.3%and mixing Ar by69%DR can reduce fueleconomy by1.2%.The maximum of in-cylinder pressure, pressure rise rate, maximum of combustiontemperature, maximum of heat release rate, oxygen concentration are reduced with increasingDR. CA10and CA50appear backward tendency. Fuel economy is slightly changed whenmixing CO2and N2at equivalence ratio but it is improved by1%when mixing Ar and it ishigher than that of CO2and N2in all DR. Fuel economy is respectively reduced by5.8%and 3.2%when mixing high DR of CO2and N2at1.4excess air coefficient. However, it isimproved by1.1%when mixing Ar.Fuel economy of inside tube dilution mode in three gases is better than inside-outside oneat1.3excess air coefficient under various DR. With increasing DR, fuel economy shows a trendof decline when mixing CO2and N2and fuel economy is the best of three gases when mixingAr in all dilution. Inside tube mode has shorter combustion duration and longer ignition delaythan inside-outside one when mixing CO2and Ar.NOx emissions of inside tube dilution mode in three gases are lower than inside-outsideone at1.3excess air coefficient. HC and CO emissions in inside tube can keep lower levelwhen mixing Ar in all DR. NOx emissions is respectively reduced by42.7%,34.8%and21.4%in inside tube when mixing106%DR of CO2, N2and Ar.Keeping fuel economy and reducing NOx emissions can be both achieved when takinglean burn technology with diluting a certain amount of dilution gas. The inside tube dilutionmode can achieve higher fuel economy and lower NOx emissions in natural gas engine. MixingAr appears better fuel economy in three dilution gases.