Effect of Flow and Gasoline Stratification on Combustion in a 4-Valve SI Engine

Visualisation of Gasoline and Exhaust Gases Distribution in a 4-Valve SI Engine; Effects of Stratification on Combustion and Pollutants

“…The test engine is a 4-valve pentroof chamber single cylinder described in earlier work1 [10] and [4]. Its geometrical characteristics are similar to the production engine, despite the presence of optical ports ( Table 1).…”

“…This distribution can be explained by the large tumbling motion on the exhaust side of the combustion chamber, being responsible for a good mixing process between the residual gases and the intake air, and the small vortex on the top of the intake side, which on the contrary makes the mixing of the residual gases with fresh air more difficult. In previous work [4] it was also remarked that the mixing of fuel with air was more difficult in the middle of the chamber. This can explain that the distribution of residual gases for an engine operating with propane is flatter than for iso-octane since propane/air mixing is perfectly homogeneous.…”

“…When stratifying the gasoline, the spark plug and the pressure transducer locations (originally 35 mm away from the centre in a direction parallel to the roof ridge) were permuted in order to favour the ignition process. Deschamps et al [4] have shown that tumble motion in the offset spark plug case is favourable for flame initiation since the low velocity (1 Ð 2 m/s) at the ignition angle (335 CAD) does not project the flame kernel on to the wall and since the higher but moderate turbulence levels for the strong tumble configuration also favours ignition.…”

“…It has already been shown that in a 4-valve engine with a pentroof chamber, fuel stratification in the direction parallel to the top of the roof can be achieved by injecting into only one of the two intake ports [2,3,4]. Biacetyl-LIF combined with LDV and combustion analyses [4] showed that by coupling the effect of intense turbulence, moderate velocity at the spark and ignition on the rich side, the performance of the 4-valves engine was greatly enhanced.…”

“…Biacetyl-LIF combined with LDV and combustion analyses [4] showed that by coupling the effect of intense turbulence, moderate velocity at the spark and ignition on the rich side, the performance of the 4-valves engine was greatly enhanced. A strong correlation level between the local mixture composition at the spark and the duration of the early phase of combustion was found for two turbulence intensities.…”