Investigation of the Impacts of Spark Plug Orientation on Combustion Stability under Lean SI Operation 2020-01-1121
The increasingly stringent restrictions on vehicle emissions and fuel consumption are driving the development of gasoline engines towards lean combustion. Increasing ignition energy has been considered an effective way to achieve lean operation conditions. To further improve the lean limit of engine combustion, the influence of the spark plug orientation on the combustion stability under lean operation should be explored. In this investigation, the original machine spark plug orientation, 90 degrees clockwise rotation, and 180 degrees clockwise rotation are studied to analyze the impact of spark plug orientation. The combustion experiment was carried out under the condition of low excess air ratio of the original machine and high excess air ratio with a 450 mA high energy ignition. It is found that changing the orientation of the spark plug had little effect on combustion at low excess air ratio; however, under high excess air ratio (ultra-lean operation), spark plug orientation had a great influence on combustion stability. The combustion stability can be significantly improved when the spark plug orientation is vertical to the intake direction. What’s more, we found that when the engine speed was low as 1000rpm, the effects of the spark plug orientation were not very clear. However, when the engine speed increased to 2000rpm, the lean operation limit can be improved from an excess air ratio of 1.78 to 1.96 by adjusting the orientation of the spark plug.