Effects of fuel injection and intake airflow on direct-injection spark-ignition combustion.

摘要

The DISI (Direct-Injection Spark Ignition) spray characteristics, in-cylinder airflow motion, and engine combustion were investigated experimentally. The engine combustion chamber had the injector and spark plug at the center of the pent-roof. Spray-guided air-fuel mixing scheme was applied.; For spray characterization, Light Extinction technique was used. Spray penetration, cone angle, and overall SMD (Sauter Mean Diameter) were found, by utilizing Nd:YAG laser as a light source. For in-cylinder airflow experiment, a one-dimensional hot-wire probe was used. Airflow velocities at 19 locations in the combustion chamber were measured, and the 3-dimensional mean velocity as well as the turbulent intensity were calculated. The engine combustion test includes obtaining COV of imep and measuring NOx, CO₂, CO emissions. Both early injection case (start of injection being 270°CA BTDC) and late injection case (start of injection being 120°CA BTDC) were tested.; By comparing the results from the three stages of experiments, the effect of spray and in-cylinder flow on the engine combustion was studied. It was shown that for the early injection case in which the start of injection was at 270°CA BTDC, the most of the droplets from the injection were vaporized before the spray reached to the top of the piston head, and the combustion chamber had homogenous charged air-fuel mixture, with help of a strong turbulence. For the late injection case in which the start of injection was at 120°CA BTDC, poor engine combustion due to the misfire was shown. Because there was not a swirl motion in the combustion chamber, the rich region of the air-fuel mixture was not confined to the center of the cylinder where the spark plug was located at. To improve combustion performance of this type of engine, a suggestion was made.