Reduction Of Smoke Emission From Diesel Engine In Acceleration Process With Electric Supercharger

The diesel engine for vehicle is increasing because of its high fuel economy, but most vehicles with diesel engine frequently produce black smoke when starting up and accelerating on the road. With dieselization of automobiles which make the number of diesel engines increase, this problem becomes serious in cities.The essential reason producing smoke is that the air-fuel ratio declines at the transient process during the sharp acceleration and load changing operations, i.e. the mass rate of the air flow into the engine don't match with the variation of fuel flow rate, which makes the quality of mixture poor and combustion insufficient. Consequently, to ameliorate the smoke emission in acceleration, the transient excess air coefficient must be boosted up during period of acceleration.To solve this problem, the method was presented to inject air into engine in acceleration with an electric supercharger. In this desertation the air injection system in fast response was designed, which consisted of the air intake shifting system of engine, and the automatic recognization system for engine operation, and the air injection unit—the electric supercharger (ES).To illustrate this method feasibility to reduction the smoke emission, the air injection system developed was applied to the naturally aspirated engine experimental station. A test bench was set up for verification of the system feasible. The air intake duct was modified, and an electrically controlled unit (ECU) for the air injection system was developed. The ECU controlled the ES and the air intake switch system through detecting change rate of the accelerator pedal position with a sensor at same time. An eddy current dynamometer was modified to meet the demand of the control system of transient operation conditions and data aquasition system.By the air injection system and the control of transient operation conditions as well as data aquasition system, the tests were conducted to study the influence on smoke emission in engine acceleration with electric supercharger injecting air. Testingl results showed that ES injecting air into engine at the acceleration or load increasing operation conditions could remarkably reduce the smoke emission, and improve the transient performance at the high load and low speed conditions. Consequently, using electric supercharger to inject air to reduce the smoke emission was feasible. Although the ES used was rebuilt from the type of J80 turbocharger of which rating speed usually is at or over the speed 100,000 r/min, it ran at the low efficiency region, however,the effects of air injection on the engine to reduce smoke emission were prominent. Testing results also showed that if the transient excess air coefficient was boosted up to 2.0 by enhancing the pressure and flux of the air intake, the higher aim to reduce the smoke and improve the transient power of engine in acceleration could be achieved.For the sake of further optimizing ES and improving the transient response performance, ES's flux and transient response characteristics were studied in experiment and numerical simulation methods respectively by the hot-wire anemometry system and computational fluid dynamic software of fluent. The research results showed that the distribution of outlet's velocity was not symmetrical, which was disadvantageous to the compressor's efficiency. According to the numerical analysis, the symmetrical distribution of outlet's velocity was caused by the inappropriate structure design of the house, and could be improved by optimizing the structure of the house. In addition, the measurement result showed that the flux was basically linear increased along with speed in the work range of ES. Upgrading the speed of ES could not only increase air injection to engine, but enhance its transient response characteristics. Research indicated that the respond time of ES was depended on the initialization set of start time and speed of the transducer, so it was important to improve the flux response of ES by advancing the start time of transducer.