Simulation Of Automobile Turbocharged Diesel Engine Under Transient Operating Conditions

With the development of automobile industry, automobile tenure increases deeply, automobile tenure increases deeply. With people's increased caring about automobile exhaust pollution problem, automobile exhaust regulations are stricter than before in many country of the world. Automobile exhaust regulations also have been issued in China. At the same time, the more diesel engine tenure increasing, the more people's caring about diesel engine exhaust pollution problem. Because automotive diesel engines often work under transient operating conditions, and the performance of automotive diesel engines under transient operating conditions is much different and some pollutant ingredient emissions are higher than that under steady operating conditions. What's more, the phenomenon is more obviously seen in turbo-charged diesel engines. Considering the real operating operations of the vehicle engines and in order to restrict the pollutant emissions, transient test cycles for diesel engines have been applied in US (EPA transient cycles) and EU (European transient test cycle).The combustion process, the emissions behavior and the performance improvement of automotive diesel engine under transient operating conditions have been a very important research field.The combustion process directly affects the power output, fuel economy, NVH and emission behavior of the diesel engine. Many similar researches have been taken before, but most of them dealt with steady operating conditions. Diesel engine under transient operating conditions are much different from those under steady operating conditions. The thesis based on the diesel CA6DL2-35E3 of FAW R&DC with turbocharger, intercooler, four-valve, six-cylinder and high pressure common rail, the diesel displacement is 8.6L. We had established model of the diesel and simulated diesel engine working process under transient operating conditions which in constant speed and increasing torque, and also analyzed and optimized the results.There are three phases in process of constant speed and increasing torque conditions. It is first phase, transient phase and steady phase. The important phase is rule of transient phase's parameter. The results is the below.1. During conditions of constant speed and increasing torque, air flow and torque have response lag; with low speed and high transient rate, the response lag time of air flow and torque is 2s, and torque has response lag according to air flow. High speed can weaken the response lag. In high speed and low transient rate, there isn't response lag.2. Diesel engine under transient operating conditions are much different from those under steady operating conditions, and they changes with the torque rising rate. In all speed conditions, with the rising of torque rising rate, air flow reduces. In speed of 1100r/min, the maximum value of air flow change is 45.726 kg/h; it is about 8.75% of the air flow in the same torque of 15s transient condition. But in speed of 1965r/min, the maximum value of air flow change is 110.492 kg/h; it is about 9.15% of the air flow in the same torque of 15s. It shows that the change of air flow relative value do not change obviously.3. During conditions of constant speed and increasing torque, with the rising of torque rising rate, air/fuel rates reduce, and it is obvious in high speed. In low speed conditions, air/fuel rate is lower than in high speed.4. In constant speed and increasing torque conditions,the maximal temperature increase with the rising of torque rising rate, but the change isn't obvious. In low speed conditions, the maximal temperature is higher than that in high speed conditions. The maximal pressure reduces with the rising of torque rising rate. Effective efficiency reduces with the rising of torque rising rate and it is not change obviously in high speed conditions.5. There are several reasons for these phenomenon. First , the air flow is still in the former cycle when fuel flow is in the next cycle. Exhaust energy produces, untill end of this cycle. Second because of compressibility of exhaust gas, pressure in exhaust pipe and exhaust energy can increase after several cycles. Third, power of turbo is larger than compressor, so compressor speed increases gradually. Compressor pressure will increase continually when compressor speed increase. Whereas, there is some cubage in intake pipe, so the pressure only increases step by step.6. In order to increase air/fuel rate, optimize performance of combustion, according to principle of air flow change fore-and-aft the research developed a formula to optimize the fuel curve with engineering theory and numerican algebra. With the formula, fuel curve is optimized, and got more ideal air/fuel rate curve, increased air/fuel rate, optimized combustion .