Impact des stratégies d'injection double sous différentes pressions sur un moteur à allumage commandé à injection indirecte à l'essence

Abstract

Indirect injection spark-ignition engines are further expanded in use due to their low production cost and low particulate emissions compared to direct injection engines. Studies have shown that by 2021, more than 50% of vehicles in the United States were still powered by indirect injection. Therefore, it is still relevant to optimize this type of engine. A review of the literature showed trials using double open-valve injection, but no recent research seems to have explored dual injection with a closed and open valve portion. Under these circumstances, the work of this dissertation must be subjected to the impact of double injection strategies under different injection pressures on a gasoline spark-ignition port fuel injection engine. In order to achieve this, a test campaign at a specific engine operating point was set up to evaluate the test bench of a single-cylinder engine including an endoscopic camera. A macroscopic spray characterization showed a decrease in the spray penetration with the increase in injection pressure for the same quantity injected. A microscopic characterization of the entire spray and the fully developed spray was performed. Analysis of the entire spray reveals a decrease in SMD between the spray head and tail showing reduced impact of aerodynamic forces on the larger droplets due to their inertia. Fully developed spray analysis showed a slight decrease in the SMD by increasing the injection pressure and reducing the injection duration, until the transient aspect of the injector became too important and as the SMD (Sauter Mean Diameter), being an indicator of the average drop size, grows. The RSF revealed less disparity in the drops size distribution by increasing the injection pressure and decreasing the injection time until the transient aspect of the injector became too great, once again. All injection strategies have showed excellent engine stability with COVIMEP not exceeding 1.5%. A decrease in specific fuel consumption of up to 10% is observed when increasing the injection pressure due to better atomization of the fuel. The double injection strategies also show a decrease in specific fuel consumption by taking advantage of better evaporation at closed valve and reduced flame initiation delay at open valve. Injection strategies do not show a major impact on fully developed combustion except for low injection pressure with a large portion of open valve injection time. The CO emissions show a decrease during double injections at 3.5 bars whereas they are stable at 2 bars. HC emissions are reduced with increasing injection pressure due to better fuel atomization and increase linearly with the portion of the open valve injection time showing the importance of time to evaporate. NOx emissions are not significantly affected by the injection strategy employed. The endoscope allowed a qualitative analysis of the soot particle emissions showing a bimodal curve of the light intensity of the diffusion flames as a function of the crankshaft position for the double injection strategies with the shortest injection times and unimodal for the others. The first mode reveals diffusion flames near the intake valve for strategies with a large portion of closed-valve injection and near the spark plug on the exhaust valve side for those with a large portion of injection. with open valve. The primary forming mechanism for the second intensity mode is found to be the locally fuel rich areas in the gas phase.

Date	20 Jan 2022
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Patrice Seers (Supervisor)