| The emission control during cold start is one of the key processes of exhaust emissions from vehicle gasoline engines at present. The essential reason for high cold-start emissions can be traced to one factor: low fuel volatility, resulting in low quality of mixture and poor combustion. Therefore,reduction of cold-start emissions can start with improving fuel volatility.To reduce cold-start engine emissions, the method was presented to preheat the intake air rapidly during cold start. On the bases of the preliminary test and the simulation, a rapid air heater was developed and then applied to the engine bench and the vehicle. The tests were conducted to study the influence on cold-start emissions with the heater heating engine intake air.In the preliminary test, effects of engine emissions at different intake temperature were investigated. The testing results showed that increasing intake temperature was favorable to the decrease of HC and CO emissions. HC emissions were remarkably decreased by heating the cold air in the intake manifold. The optimal intake temperature of 70℃could reduce emissions most. The temperature of the initially inducted fresh air significantly influenced HC emissions. HC emissions were remarkably decreased by heating the cold air in the intake manifold. These results provide scientific evidence for further studying emissions during cold start.To reduce cold-start emission and improve combustion process more effectively, based on fuel evaporation theory, three-dimensional numerical simulation of fuel evaporation in a gasoline engine during cold start was employed using the CFD software. The simulation results indicated that the most influential parameters on the fuel evaporation were: intake temperature, fuel temperature and engine speed. The intake temperature was the most influential among the three. The initial droplet size and injection timing had some effect on the percentage of evaporated fuel. The initial droplet velocity had a relatively little effect on the fuel evaporation. Increasing intake temperature not only conduced to fuel evaporation in the intake port, but also increased in-cylinder temperature, which promoted the evaporation in the cylinder fuel. It also created a favorable condition for the formation of ignition mixture.Based on rapidly heating, adopting low pressure injection and high ignition, employing a hollow cone swirl nozzle with the flow from a swirler, a rapid air heater with low cost was developed to increase the intake temperature for the reduction of cold-start emissions of gasoline engines. The heater was independently controlled by an ECU. Through the numerical simulation of the combustion and heat transfer of the air heater using CFD software and the optimization of its construction, the testing result showed that the heater realized fast heating and clean burning, but the exhaust temperature was excessively high.Through the simple modification of the oil inlet pipe and the connection between the hot air outlet of the heater and the intake pipe of the engine, the heater consumed the fuel from the fuel pump of the engine and became part of the engine air inlet system. The results indicated that a satisfied intake air temperature before engine start was obtained in 32 seconds. After engine start, the intake temperature kept high for several minutes. Preheating intake air could reduce HC by more than 33% and CO more than 11% by fueling both gasoline and ethanol-gasoline during engine cold start.A test on low temperature start-up emissions from a micro subminiature car of EuropeⅡstandard was carried out. The vehicle test showed that both THC and CO emissions were lower than the emission limit value in the EuropeⅢandⅣby using the air heater, meeting more stringent gasoline exhaust limits. In addition, the heater substantially improved the low temperature start-up performance.
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