In order to understand better the process of hydrocarbon formation and the effect of the top-land crevice and the oil layer of the cylinder liner on unburned hydrocarbons during cold start and idling periods, the temperature of the piston top-land and liner was measured. Based on the measured results, the amount of unburned hydrocarbons from the crevice and liner has been predicted. It was found that the temperature of the piston top-land and cylinder liner took about 150-200 s to reach its equilibrium state as the engine started up. The concentration of hydrocarbons from the top-land crevice and from the oil layer will be reduced to 40 and 75 per cent of its initial value respectively. It is considered that a reduction in piston thermal capacity can reduce the total unburned hydrocarbons during this transient period owing to quick minimization of the top-land crevice volume and rapid increase in mixture temperature in the crevice region.
Experimental research on the effect of excess air ratio on dynamic and emission performance of turbocharged lean-burned CNG engine. The 12 test conditions contain engine speeds of 1300r/min, 1600r/min, and 1900r/min, with 25%, 50%, 75%, 100% load separately. When keeping other combustion boundary conditions unchanged, the excess air ratio has little effect on engine output torque at almost all test conditions, but has obvious effect on CH4 and NOx emission. With the excess air ratio increasing, the emission of CH4 has increased while the NOx emission has decreased significantly. When the λ value is in the range of 1.4-1.45, the emission level is lower.
The objective of this research is to introduce the main gasoline direct injection vehicle particulate emissions characteristics researches in the world. Many investigations of particulate sizing and number count from gasoline direct injection (GDI) vehicles at different driving cycles were performed. Lots of particulate emissions are measured for FTP-75, NEDC, HWTET, SC03, and US06 cycles and these cycles can reflect different aspects of the particulate emissions. In some papers, both engine-out and tailpipe emissions were measured. Some investigation showed high sensitivity of the particulate number or size distribution to changes with the engine control parameters including A/F, ignition timing, EOI and so on.On the whole, the particulate number during different Driving Cycle is shown along with further analysis of the transient particulate emissions. The cold start process obviously affects particulate formation. Even beyond cold start, the particulate number emissions decrease as the test progresses. The results coming from the particulate measurement system sampling directly from the exhaust showed very rapid increases in particulate emissions during engine transients.
Experimental study on the combustion and emission performance of turbocharged lean-burned CNG engine by the ignition time. Speed of the engine is 1340r/min,1615r/min,1890r/min,with 25%, 50%,75%,100% load. Results show that when keeping other combustion boundary conditions unchanged, the effect of the ignition time on engine output torque and CH4 is little,the effect changes as speed varies from low speed and load conditions to higher level.However,the effects of ignition time on NOx emissions are huge.With the backward changes of the ignition time,NOx emissions has decreased significantly.
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