Effect of spark timing on the pre-chamber jet ignition in a lean-burn natural gas engine

Abstract

An enhanced combustion concept, pre-chamber jet ignition can provide high ignition energy and a wide dispersion of ignition sources, thus improving combustion performance and realizing stable lean combustion. However, the ignition performance of the pre-chamber jets depends strongly on the pre-chamber combustion process and is sensitive to many factors. Therefore, this paper will explore the impact of spark timing on the pre-chamber combustion, turbulent jet characteristics, and main chamber combustion performance by CFD simulation based on an active pre-chamber natural gas engine. The in-cylinder flow and combustion processes of the engine are calculated with the fuel-air equivalence ratio of the main chamber maintained at 0.5, and the spark timing varied from 684°CA to 708°CA with a step of 3°CA (compression top dead center is 720°CA). The results show that, in the present engine operating point, the pre-chamber combustion heat release rate is improved when the spark timing is retarded from 696°CA to 705°CA, and the injection velocity of the pre-chamber jet accordingly increases. As the spark timing continues to be delayed until 708°CA, the pre-chamber combustion deteriorates, and the injection velocity of the pre-chamber jet decreases. Under the combustion phase CA50 no more than 725°CA and the combustion duration CA5-90 fixed around 30°CA, the IMEP will maintain a relatively stable value when the spark timing is delayed from 693°CA to 705°CA, in the meantime, the NOx emission decreases with the delay of spark timing. Therefore, on the premise of ensuring engine power performance, it is a feasible scheme to delay spark timing to reduce NOx emission for the natural gas engine with an active pre-chamber.

Numerical Investigation of the Operating Characteristics of the Passive and Active Prechamber Jet Ignition in a Natural Gas Engine

“…Therefore, the established model and the adopted mechanism can predict the flow and combustion process in the natural gas engine with prechamber ignition. This numerical model can be used to simulate the performance of the prechamber ignition system with an active prechamber, and its effectiveness has also been verified in our previous research work. , …”

“…In this study, the CFD program CONVERGE is used to simulate the flow and combustion process in the single-cylinder natural gas engine. Figure shows the calculation domain at the top dead center (TDC) . It primarily contains three parts: intake-exhaust system, main chamber, and prechamber.…”

“…The engine speed is 1000 r/min, and the fuel of the main chamber and prechamber is methane. Our previous research summarized the initial conditions and boundary conditions of the simulation. , The inlet of the intake port is set as an inflow boundary condition. The experimental pressure of the intake port is used as the pressure boundary condition.…”

“…The schematic diagram of the test platform is shown in Figure . The main chamber uses a premixed intake charge of air and natural gas.…”

“…The schematic diagram of the test platform is shown in Figure 1 . 49 The main chamber uses a premixed intake charge of air and natural gas. Natural gas mixes with air in the air–fuel mixer 14 to obtain a uniform mixture.…”