Study On Stratified Lean-burn Of Small Non-road Spark-ignition Engine

Saving energy and protecting environment are important factors to realize sustainable development of human society. To satisfy the requirements of internal combustion engine with low fuel consumption and low emissions, lean-burn is one of the typical engine technologies developed by researchers. Not only can gasoline engine lean-burn technology reduce fuel consumption, but also can greatly reduce HC and CO emissions. With the growing of small non-road spark-ignition (SI) gasoline engine production in recent years, the more strict emission regulations were developed and implemented in United States and Europe, which formed technical barriers to small gasoline engine industry and reduced the exports. To do the lean-burn research on small gasoline engine is meaningful, which can decrease fuel consumption and reduce harmful emissions.A lean-burn mode of SI engine is proposaled which is called Supplemental side Air Injection (SAI) mode. It is based on an advantage that combined motion of airflow has a faster burning speed and better combustion characteristics. The SAI port is bored through one side of the engine cylinder wall and connected with an induction channel through a solenoid valve. In portions of intake and detonation strokes, compressed air is introduced into cylinder to produce strong swirl while combustible mixture is inhaled through intake valve. Compressed air for SAI is provided by an air compressor and its intake timing is controlled by a magnetic valve. After that, the rich mixture from SAI port will be kept in the upper part of the cylinder and around the spark plug, and the lean mixture will be kept in the lower part. Then a combined airflow motion produces in the cylinder, thus homogeneous stratified lean-burn is obtained in non-road small SI engine.To study on 168F small non-road SI gasoline engine, the implementation and affection on emissions and fuel economy of SAI which is proposed to obtain lean-burn and to ensure a stable combustion are studied in this paper. Overviews of small gasoline engine and emission regulations and research on stratified lean-burn domestic and overseas are introduced firstly, and then analyzed intake and exhaust organization of small gasoline engine, airflow development, characteristic and discipline of mixture generation and its combustion. Secondarily, consideration on structural characteristics and operational states of small engine, the paper introduces stratified lean-burn implementation on small engine, which studies theoretically on its feasibility and mechanism of formation with SAI mode. Then an inlet-cylinder-outlet model of small engine is builded with Pro/E 3D software and imported into AVL FIRE (CFD) numerical simulation software, next to be analyzed coupling of the main and SAI intake and combustion processes, and then obtain the key structural elements of SAI. Last but not the least, this study carries out comparative experiment that fuel consumption as well as emissions are experimentally investigated on prototype and SAI engine with different working conditions.The results show that the SAI engine achieves stable work at most of the working conditions. To compare with the prototype engine, the SAI engine has a higher combustion cyclic efficiency and lower fuel consumption at small-load and medium-load operating conditions. Oxygen concentration is higher than in prototype engine cylinder while the SAI engine work at the normal work conditions, the combustible mixture in cylinder has been fully burned. HC and CO emissions are reduced significantly in the oxygen-rich state. Meanwhile, NOx emissions generally raise and increase with load increasing.