Research On Combustion Mechanism And Performance Of Gasoline Engine With O₂/CO₂ Mixed Intake Air

As the vehical number increases and the emission regulations are stringent, innovation on traditional energy technology has become a focused issue. And the engine with oxygen enriched intake air, of superior energy-saving and environmental protection effects, has been broadly concerned. As combustion-supporting gas or non-combustion-supporting gas can be respectively mixed into the intake air, different impact on engine performance is caused; that is, if combustion-supporting gas is mixed into intake air (such as O2), the motive performance and fuel economy will be raised, but NOx emissions will be much higher; if non-combustion-supporting gas is mixed into intake air (such as CO2), the motive performance and fuel economy will worsen, but NOx emissions will be much lower. Therefore, in this paper, with the objective to improve combustion and reduce emissions, according to the main means of numerical simulation and bench test, and based on the property of oxygen enriched intake air in gasoline engine, combustion mechanism and emission performance of chemical reaction kinetics, improvement impact of mixed O2 on combustion and emission of gasoline engine low temperature cold start, and optimum proportioning of O2/CO2 in intake air, etc., the following researches are conducted:First, based on theoretical analysis, from the perspective of chemical reaction kinetics, the impact of O2 rate increase on combustion products and intermediate products in isooctane oxidation process is analyzed; and based on combustion mechanism and emission performance of oxygen enriched intake air gasoline engine, innate characteristics and principle of combustion process of oxygen enriched intake air gasoline engine is summarized. By increasing O2 rate chemical reaction speed in gasoline engine is raised, generation volume and range of major intermediate products such as OH and CH2O, etc. in combustion increase, thus .the fuel is burnt more completely, the combustion temperature and combustion pressure increase, and CO2 caused by incomplete combustion and unburned HC emissions are reduced. However, at the same time the increased O2 rate improves combustion in the cylinder, the significantly increased NOx emissions problem is also caused. Therefore, in this paper, with the method to reduce CO2 mixed in intake air, the high NOx emissions produced by the oxygen enriched intake air are prevented.Second, according to proportioning of O2/CO2 in intake air of gasoline engine, the relevant research contents and research method are determined, and the relevant test system and test instrument are applied to build test-bed of mixed intake air gasoline engine performance and test-bed of low temperature cold start for experimental research.Third, HC, CO and NOx emission under different O2 rates within 60s after the low temperature cold start, as well as impact on combustion status in the cylinder is analyzed; and according to the running status of gasoline engine after oxygen enriched intake air applied, the optimum oxygen enrichment proportional range is chosen. From the research, from the perspective of control emission within 60s after the low temperature cold start,23%-25% oxygen enriched intake air is more appropriate for low temperature cold start of gasoline engine in this experiment.Fourth, based on the different steady working conditions and the different mixed intake air constituent conditions, the testing program is designed, and the power performance, economy performance, combustion characteristic and emission performance are tested. Gasoline engine performance with intake air of O2 and O7/CO2 is respectively researched; the emphasis is on research of matching between intake air constituents and engine working conditions, and with the premise that engine power and fuel consumption reach required value, HC, CO and NOA emission should be reduced as much as possible. From the test result of load& speed characteristics in oxygen enriched intake air gasoline engine, the 23%-25%O2 rate is the optimum oxygen enriched intake air proportion. As O? rate is further raised, NOx emission can be doubled, while other beneficial indicators range ability obviously weakens. Addition of 2% of CO2 into the 25% O2 will not only boost the motive performance and fuel economy, but also reduce HC, CO and NOx emission, and increase the combustion temperature.Fifth, with CHEMKIN, the mechanism of isooctane Chemical Reaction Kinetics is imported, and combustion process with different intake air constituents is simulated, the model accuracy is verified based on test, impact of intake air constituents on intermediate reaction groups and isooctane oxidization mechanism is analyzed, thus insufficiency of experimental study is supplemented, and change of combustion process of oxygen enriched gasoline engine after compression ratio and excess air ratio altered is also analyzed.