| It's well known that there are always great challenges we have to face in the 21st century--the transportation energy sources and environment pollution. However, with the increasing amounts of vehicle in our country, the situation becomes more and more serious. Reducing the fuel consumption and engine emission are two major questions had to be dealt with for further engine development.Conventional engine include spark ignition engine and compression engine. The combustion of spark ignition engine is premixed homogeneous promulgation combustion. The mixture is ignited by the spark. Due to the limits of the characteristic of gasoline and knock of the spark ignition engine, the he Compression Ratio (CR) in the spark ignition engine is small. This leads the decrease of the thermo efficiency and the formation of many Nitrogen Oxides (NOx) and unburned gases. On the other hand, the Spark ignition engine controls the load through the throttle, this leads to the decrease of mechanical efficiency in the middle load. The Spark ignition engine's energy efficiency is 70% of the counterpart in the Diesel engine. This is the insurmountable limitation of the Spark ignition engine Diesel engine's combustion is diffusing combustion. The mixture starts 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. Because the temperature of diesel engine is very high, NOX emission is vast. The lean of oxygen at flame region with high temperature and consistency of mixture leads to the occurrence of a mass of PM and so there is a limit in the emissions of PM and NOX in diesel engine.The engine technology of HCCI (Homogenous charge Compression Ignition) is a new engine concept which raises world-wide attention.HCCI(Homogenous charge Compression Ignition)is a new combustion mode .The mixture, composing of the fuel, air and the recycled exhaust gases (EGR), is compressed, auto-ignited, combustion and work. It has the potential to be highly efficient and to produce low NOx, carbon dioxide and particulate matter emissions .It experiences, however, problems with cold start, running at idle and high loads that together with controlling the combustion over the entire speed/load range limit its practical application. A solution to overcome these problems is to operate the engine in'hybrid mode', where the engine operates in spark ignition (SI) mode (or diesel mode-CI) at a cold start, idle and higher loads and can switch to HCCI mode at low and medium loads,. Between the mode transition of HCCI and SI, however, the engine speed and torque changes in an unacceptable range as a result. The objective of this paper is to present a investigation of using electrical control system for a transition from SI to HCCI to SI mode using ethanol fuel at different engine speeds ignition timings, injection timings, and a control strategy of the mode transition between SI and HCCI and SI modes , aiming to perform mode transitions smoothly.1,The experiment had been carried out on a modified single cylinder engine from ZS 1105 diesel engine, the modified parts include , added electronic control spark ignition , ethanol fuels inject system and , so that mode transition can be preformed, while keeping the engine equipment drivability, combustion stability.2,Electronic control system was used to investigate the influences of the ethanol mode transition in different conditions such as different speed, ignition timing and injection timing. The results indicate that at the boundary condition of HCCI combustion, ignition timing is more influential on the transition process than injection timing. as the ignition timing advanced, the combustion phasing delayed, the peak pressure in the cylinder decreased, the fluctuation of cylinder pressure increase. As the ignite timing increases , the phasing of combustion timing become earlier, the engine torque increase, the fluctuation of cylinder pressure decrease. however , as the ignition timing retard, engine's torque decrease at the SI mode, because there is bigger difference between the torque of two combustion mode, the engine speed and torque can't maintain the same value. So at different engine speed, there is a optimal ignite timing. At the optimal ignite timing the engine cycles of mode transition is least, and the fluctuation of the engine speed and torque is very low.3,Based on the above results and exploring through the experiments, we put forward an active control strategy based on throttle position, oil injection and ignition timing, and achieve smooth transition of the SI-HCCI combustion mode. The control strategy is that, at the SI-HCCI combustion mode transition of misfire boundary, when the throttle open to the target position, the air/fuel mixture is become from thick to thin. When the throttle wide open, the oil rate is less than the origin. From the HCCI mode to the SI mode, the throttle back to the original position. The knock boundary is differ from misfire boundary, from SI mode to HCCI mode, the throttle move first, when the throttle move to the target position, decreasing the oil to the target rate, meanwhile, the throttle wide open. From the HCCI mode to the SI mode, back to the original position. At the whole mode transition, the fluctuation of dual combustion mode transition has been resolved by the control strategy. So the active control can maintain the same value of engine speed and torque.The experiments have validated the fact that: at the mode transition of the ethanol fuels of dual combustion, from SI to HCCI to SI mode , engine can maintain the same valve of speed and torque by using the active control with throttle position, fueling rate and ignition timing. |
