Effects Of Enriching Fuel Property On The Performance Of Natural Gas Engine With Thermochemical Fuel Reforming Combustion Mode

Natural gas has caused much attention in recent years as a fossil fuel and it is considered as one of the most promising alternative fuels for internal combustion engines.Natural gas has its unique advantages as an engine fuel:clean combustion with low pollutant emissions,rich in reserves with low price.However,natural gas also has some shortcomings such as low energy density and slow flame propagation speed,which makes the naturally aspirated natural gas engine less efficient.Optimizing the combustion of natural gas engines is expected to solve such problems.Therefore,optimizing the combustion of natural gas engine can improve the thermal efficiency and reduce emissions,thus mitigating energy crisis and reducing environmental pollution.In-cylinder thermochemical fuel reforming(TFR)combustion mode involves running one cylinder rich to generate much reformed gas,such as hydrogen and carbon monoxide.And then the reformed gas was introduced back into each cylinder to optimize the combustion.This paper was based on a four-cylinder,port-fuel-injection,turbocharged,spark ignition natural gas engine to study the effects of enriching fuel property on the performance of the engine.Enriching fuel injectors(including a liquid fuel injector and a gas fuel injector)were installed at the intake manifold of the fourth cylinder,and the exhaust gas from the fourth cylinder was introduced back into the intake manifold through a cooler and distributed to respective cylinders.In this paper,methanol and ethanol with different carbon-hydroxyl ratio,n-propanol and isopropanol with hydroxy isomeric,n-heptane and isooctane with different chemical activities,were researched to figure out the effects of enriching fuel property on the engine performance.The results showed that the engine economy and emissions were better than those in the case of methane enrichment when methanol and ethanol with different carbon-hydroxyl ratio were enriched.The performance of the engine was better with methanol enrichment than ethanol enrichment.With methanol enrichment,the brake specific gas consumption of the engine was reduced,and the rich combustion limit was wider.Further methanol enrichment could reduce carbon monoxide,hydrocarbons and nitrogen oxides emissions.The stability of the engine with methanol enrichment was better than ethanol and methane enrichment by sequence.The effect of n-propanol and i-propanol enrichment with hydroxy isomeric on the performance of the engine showed that the brake specific gas consumption,the hydrocarbon emissions of the engine,and the NO_x emissions of the engine were lower than those of methane enrichment.But the difference in carbon monoxide emissions of was small with these three fuels enrichment.When n-propanol enrichment,the brake specific gas consumption,hydrocarbon emissions,and NO_x emissions were lower than i-propanol,but the effect is not significant.The effects of high-activity fuel n-heptane and low-activity fuel isooctane enrichment on the performance of the ignited natural gas engine were studied.The results show that the stability,economy and emissions of n-heptane and isooctane are better than that of methane enrichment,and the stability and economy of n-heptane enrichment is better than that of isooctane enrichment.Finally,it was found that the hydroxy isomerism had little effect on the performance of the engine,while the carbon-hydroxyl ratio and fuel activity had an influence on the performance of the engine.The lower carbon-hydroxyl ratio methanol promotes the formation of hydrogen and carbon monoxide in TFR cylinder.For engine stability,the lower carbon-hydroxy methanol and high activity n-heptane enrichment improves the stability of the engine,and the positional heterogeneity of the propanol hydroxyl has little effect on the stability of the whole machine.For brake specific gas consumption,low carbon-hydroxyl methanol and high activity n-heptane enrichment are lower than other enriching fuels.For emissions of the engine,liquid fuel enrichment can significantly reduce NOx emissions,and THC and CO emissions are not significantly reduced.Methanol can be further enriched to a greater extent to simultaneously reduce NOx,THC,and CO emissions.