EGR Gas Research Articles

CFDによる予混合気不均一性がHCCI燃焼におよぼす影響の解析(予混合圧縮着火燃焼と新燃焼(1),予混合圧縮着火燃焼と新燃焼)

A combustion process in an HCCI engine has been simulated using CFD code in conjunction with a 5-step global reaction model for hydrocarbon fuels. The Large Eddy Simulation (LES) was employed to describe turbulent transport. The calculations were performed for homogeneous and heterogeneous mixtures of EGR gas and fuel-air mixture. From the calculation results of combustion process, it is found that the heat release rate for the heterogeneous case is more moderate than that for the homogeneous case.

Improvement of Stratified Combustion by a Large Amount of Hot EGR (Reduction of Unburned Hydrocarbons)

Unburned hydrocarbons from a direct injection stratified charge engine were greatly reduced by a large amount of hot EGR. A hydraulically controlled variable valve system was used to realize the hot EGR. Almost all the amount of required EGR gas for the NOx reduction was supplied directly from the previous cycle through the exhaust or inlet valves. Two kinds of recirculation were examined in this test. The first was the recirculation through the exhaust valves, which opened additionally during the suction stroke. Another was the recirculation through the inlet valves. The exhaust gas was pushed back to the port during the exhaust stroke through the additionally opened inlet valves and re-induced in the next cycle. Although both methods have the same ability to reduce HC emissions, required EGR was less in the latter method.

1801 低温 EGR 時のピストン摩擦現象と腐食摩耗

If it is intended to apply cooled EGR to heavy-duty diesel engine for a more reduction of NO_x emission, it will also be necessary at the same time, to reduce corrosive wear induced by condensed water including the acids on piston rings and cylinder liner due to cooled EGR. This study aims at making clear the effects of condensed water supplied to the combustion chamber on the cylinder oil film formation when the temperature of EGR gas becomes lower. The piston friction has been measured under various temperatures of EGR gas for the verification of lubricating condition of piston and piston ring. As a result, it is found that the piston friction spiky increase just after TDC where the EGR gas temperature becomes lower and that the condensed water easily reaches the cylinder wall surface through the oil film.

Effects of EGR on direct injection gasoline engine

A large amount of EGR was introduced into a direct injection gasoline engine. According to the increase of EGR rate, it was found that the combustion at the late period is hastened in spite of reduction of the initial burning rate. In consequence, both HC and NO x were reduced by EGR. This suggests that the effect on acceleration of the leaner mixture's flame propagation by hot EGR gas becomes varied under the condition of the stratified mixture's stabilized ignition.

Piston friction force with EGR activated

The piston friction force increases in the latter half of the compression stroke where the EGR system is activated, while the force is decreased at each stroke center. This is due to the soot contained in the EGR gas. Although tho reduction of piston friction force at the stroke center reduces the piston friction loss, the increase of friction force in the latter half of compression stroke is caused by the friction coefficient, which becomes higher at this point. Hence it can be anticipated that wear on the piston rings and cylinders would increase accordingly. The change in piston friction force characteristics with the mixture of soot is quite an interesting phenomenon, and further studies on this phenomenon, are expected.

Improvement of Natural-Gas-Fueled Spark Ignition Engine Performance. Experimental Study on Effect of EGR Utilization.

An experimental study was conducted to investigate the effect of EGR on combustion and exhaust emission characteristics of a spark-ignited supercharged stoichiometric gas engine in order to achieve a high BMEP equivalent to that of diesel engines. A single-cylinder test engine of 4-stroke-cycle was used. EGR gas was completely mixed with intake air before being introduced into the compressor. The results indicate that the dry EGR utilizing drained exhaust gas improved the maximum mean effective pressure as well as the specific fuel consumption over the whole load due to improved knock characteristics of the unburnt mixture, increased specific heat ratio (x), and reduced heat loss. Further experiments were conducted to identify the effect of humidity in the mixture on the engine performance.

Study of fuel economy improvement through control of intake valve closing timing: cause of combustion deterioration and improvement

An investigation was made of the effects of intake valve closing timing on the spark-ignition engine combustion when the closing timing was varied for the purpose of reducing pumping loss. It was found that the principal cause of combustion deterioration was a drop in cylinder gas temperature and pressure, which was traced to a decline in the effective compression ratio and to a reduction in EGR gas and residual gas fraction. It was also observed that increasing the residual gas fraction worked to mitigate the deterioration of combustion.