Experimental Study On Improvement Of Diesel Combustion And Emissions Using Flash Boiling Injection

With severe worldwide energy crisis and stricter exhaust emission law and regulations, as one of the main fuel consumption and environment pollution sources, internal combustion engine are being paid more and more attention. As one of the new combustion types, homogeneous charge compression ignition (HCCI) is being highly regarded as a research focus.A new method of utilizing the flash boiling injection effect of high temperature diesel fuel to intensify the fuel spray evaporation and mixing for HCCI diesel engine was proposed in this thesis. Firstly, a visual test bench of quasi-stable state fuel injection spray was established, and the influence of high temperature flash boiling injection of diesel fuel on Sauter Mean Diameter (SMD) was tested by laser droplet size analyzer. The SMD distributions of diesel engine on different injection pressure and fuel temperatures were compared to reveal the microscopic characteristics of flash boiling spray and on the meanwhile, the flash boiling spray effects of decreasing the fuel droplet diameter, and improving the spray mixture were verified.A Model ZS195, single cylinder, direct injection diesel engine was used to test the HCCI combustion. The heating and temperature controlling system of high pressure fuel supply pipe was installed following the fuel injection pump which has been retrofitted for HCCI fuel supply system. The combustion and exhaust emission of HCCI diesel engine were tested under different fuel temperatures, and the effect of high temperature flash boiling was clearly demonstrated by the test results, the optimum diesel fuel temperature range in terms of fuel economy and exhaust pollution were obviously improved. The fuel consumption rate and exhaust emission increased when the fuel temperature surpassed the optimum range, since the combustion was deteriorated by after burning which was caused due to fuel injection angle delay. Engine comparison tests of different fuel supply advance angles, injection pressure, and injector orifices were carried out to ascertain the influence of engine structure and operating parameters on the combustion and emission characteristics. As showed in the test results, the HCCI combustion of diesel engine was realized by high temperature flash boiling spray, while enlarging the fuel supply advance angle to 32°CA BTDC, and increasing the fuel temperature to 160℃~ 200℃, and the fuel consumption rate and exhaust emissions were improved to a certain extent.