The influence of combustion system parameters on engine performance. Fuel supply advance angle and fuel injection pressure test results show that the best fuel supply advance angle (CABTDC) of dimethyl ether during operation is: 19° under calibration conditions and 15° at low speed. This is 6°-9° smaller than the best fuel supply advance angle (25°) of diesel in operation; when the injection pressure of dimethyl ether is 15MPa (lower than the injection pressure of diesel 18MPa), the thermal efficiency is highest. This is because dimethyl ether has a higher cetane number, lower auto-ignition temperature and better atomization performance than diesel. Plunger Diameter The effects of three plungers with diameters of 8.5mm, 9.0mm and 9.5mm on the thermal efficiency of the engine were tested. The thermal efficiency η of the engine with different diameter plungers varies with the average effective pressure P. From this, it can be seen that the thermal efficiency of the engine increases with the increase of the plunger diameter. This is because the low calorific value and liquid density of dimethyl ether are only 64.7% and 80% of diesel. The increased fuel supply per cycle requires an increase in the diameter of the plunger to shorten the fuel injection duration to improve the performance of the engine.
Nozzle form and its depth into the cylinder The influence of 5 different forms of nozzles on the thermal efficiency of the engine was tested. Among them, the 5×0.32mm nozzle is the best, and the highest thermal efficiency is obtained. Compared with the 4×0.30mm nozzle used in the original machine, it has an increase in the number of nozzle holes, an increase in diameter, and an increase in the total flow area. The nozzle of this structure can be better with low intake swirl ratio (the best intake swirl ratio when using dimethyl ether is 1.4～1.8, which is much lower than the original engine swirl ratio 2.3) and large circulating supply Matching the amount of oil is conducive to the formation and combustion of the dimethyl ether mixture. Studies have shown that the best length of the nozzle to extend into the cylinder when using dimethyl ether is 5mm, which is longer than 3mm when using diesel. This is because dimethyl ether has good evaporation and atomization performance, and the spray cone angle formed by the fuel injected into the cylinder is large. In order to prevent the liquid fuel from hitting the bottom surface of the cylinder head and causing combustion deterioration, the length of the nozzle extending into the cylinder is required. Increase.
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