| As it's the advantages such as high power exchange efficiency, high power density and good mobility, the engines have been applied in many businesses in a large scale, especially in automobiles and others movable equipments. From the birth of the engine, it's got to be high level concerning the major parameters at present, for example, power performances, economic performances and durability. But, under the background of the global energy crisis and environmental protection, the engine business is facing the austere challenge. Whether the engine can meet the requests of the energy and environment is critical for the business to survive in the 21st century. Although the applications of the emission law and oil consumption law in developed country, the engine technology had advanced greatly. Compared with the 1970s, the energy efficiency and poisonous emissions have been improved greatly, the poisonous emissions had been decreased more the 90 percentages. But, with the economy development and society advance, the limits to the emissions are more and more strict, the emission law is more and more strict. This is a challenge task to the engine business to decrease the poisonous emissions. Otto engine's combustion is of premixed homogeneous promulgation combustion. The mixture is ignited by the spark. the Compression Ratio (CR) in the Otto engine is small. So this decreases the thermo efficiency and leads to the formation of many Nitrogen Oxides (NOx) and unburned gases. Also, the Otto engine control the load through the throttle, this leads to the mechanical efficiency decrease in the middle load. The Otto engine's energy efficiency is 70 percentage of the counterpart in the Diesel engine. This is the insurmountable limitation of the Otto engine. Diesel engine's combustion is of diffusing combustion. The mixture realize ignition at the end of the compression stroke. Because of the short time to form the mixture, the mixture of the fuels and air isn't homogeneous. This leads to the formation of the high temperature flame region, and the formation NOx and Particle Material (PM). This is the insurmountable limitations of the Diesel to lower the poisonous emissions. How to breach the traditional Diesel and Otto engine's limitation of emission and energy efficiency, search the new combustion of the petroleum and substitute fuel is the challenge confronted to the business and the workers. Homogeneous Charge Compression Ignition (HCCI) is of a new combustion. The mixture, composing of the fuel, air and the recycled exhaust gases (EGR), is compressed,auto-ignited,combustion and work. In this combustion, the engine has high thermo efficiency corresponded with Diesel engines, meanwhile, the emissions of the NOx and PM are small because of its unique homogeneous charge and low temperature combustion. It is likely to surmount the limitations of the energy efficiency and poisonous emission. It's been the hot topic in the business in the world, in 2002, this topic had been projected as the national important basic research project in our country. This author had carried out experiment concerning the HCCI combustion of ethanol under the project 973 national important basic research project——The boundary conditions of alcoholic fuels combustion and critical question concerning the fuel chemistry's control in harmony. The ethanol is easy to realize evaporation and form homogeneous charge. But with its low cetane number, it's hard to realize the compression ignition of the ethanol. There are two methods to realize low cetane number fuels'HCCI combustion in engine, one is to adopt the warm-up system in the induction, after the warm-up process, the homogeneous charge realize auto-ignition and combustion in the latter period of the compression stroke, the other is to adopt the internal EGR system. Under the help of the heat in EGR, the mixture's temperature at the end of the compression stroke is higher than the auto-ignition temperature. Compared to the warm-up system, when adopting the internal EGR system, To realize internal EGR, it's necessary that there should have the Variable Valve Timing (VVT) system, but at present, there isn't mature technology in this topic in the country, so the author adopt the warm-up system to carry out the experiments in ethanol's HCCI combustion.The author has designed the induction warm-up management system, selected the warm-up unit, decided the last scheme to realize the quick and steady temperature's control and designed the electrocircuit and the executable outfits. After the preparation of the warm-up system, the author has carried out the experiments to test the system's response to the temperature. The results show, this warm-up system can realize quick and steady response to the temperature, it meets the requests. In the engine added with this system, HCCI combustion had accomplished. Then under the help of the warm-up system, the author has carried out experiments to search induction temperature's influences to the ethanol HCCI combustion. The results show, the induction temperature does great influences to the ethanol's HCCI combustion. when keep the engine speed and air/fuel equivalence ratio constant, as the temperature increases, the phasing of combustion occurs earlier, combustion duration becomes shorter, the rate of combustion increases, the rate of pressure rise increases, the maximum cylinder pressure increases, the combustion efficiency increases, the indicated efficiency increases, but as the temperature increase further, the indicated efficiency decreases. There is a maxim indicated efficiency related to certain temperature. So the author puts forward to the concept of the prime induction temperature (PIT). If the induction temperature is less than the PIT, the indicated efficiency increases as the induction temperature increases, if the induction temperature is higher than the PIT, the indicated efficiency decreases as the induction temperature increases. Meanwhile, the results show that air/fuel equivalent ratio does has great effects to the ethanol's HCCI combustion. When keep the engine speed and induction temperature constant, as the air/fuel equivalent ratio decreases, the phasing of combustion occurs earlier, combustion duration becomes shorter,the rate of pressure rise increases, the maximum cylinder pressure increases, the combustion efficiency increases and the indicated efficiency increases, the PIT decreases. In the last, the author got the MAP of the PIT related to the engine speed and air/fuel equivalent ratio. This provides the scientific data and basic technical measures to realize the transition between the SI and HCCI combustion. |
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