An investigation for reducing combustion instability under cold-start condition of a direct injection gasoline engine

Abstract

In order to meet recent stringent emission regulations, the exhaust catalyst should be heated as early as possible to activate the purifying reactions. In a direct injection spark-ignition engine, a combination of late fuel injection during the compression stroke and late ignition in the expansion stroke is a common strategy to quickly raise exhaust gas temperature for subsequent rapid activation of exhaust catalysts. However, this approach under cold start-up of an engine often results in incomplete and unstable combustion. In this study, to explore the conditions of stable ignition and combustion, the effect of injection timing on indicated mean effective pressure and early combustion duration (MBD0.5) are first investigated by an analysis of the pressure indicator diagram. As this analysis shows a strong correlation between indicated mean effective pressure and MBD0.5, the mechanism of initial flame propagation is investigated intensively using optical diagnostics. Namely, mean equivalence ratio of mixtures in the propagating flame front is measured by focusing on the ratio of C 2 * to CH* emission intensities. The flow velocity and turbulence intensity around the spark electrode are measured by the back-scattering laser Doppler anemometry. Two major conclusions are derived from this study: First, when the injection timing is retarded, the mean equivalence ratio increases as the time for the injected fuel to travel and diffuse is shortened. The most preferable mean equivalence ratio for fast initial combustion is found to lie in a range from 1.2 to 1.4. Second, when the second injection timing is retarded further, the mean equivalence ratio increases exceeding 1.4, and this results in slower and more fluctuated initial flame propagation. But, if the turbulent intensity is increased by means of the spray induced air motion, the slowed initial combustion can be recovered.

A detailed multidimensional simulation for the cold start process of a gasoline direct injection engine using a fractal engine simulation model

“…Moreover, the catalysts in the after-treatment system cannot be fully operational because the temperature is below the light-off temperature of around 250°C. 2 Different experimental [3][4][5][6] and simulation [7][8][9][10][11] studies have been used to focus on what happens during the cold start process and what may be done to reduce the emissions. Efforts are needed in the experiments to eliminate the wall wetting and maintain a cold wall to mimic a cold-start environment, which introduces extra work and difficulties.…”

Investigations of split injection properties on the spray characteristics using a solenoid high-pressure injector

“…11,12 The local equivalence ratio near the spark plug also increases as the distance between the spark plug and the piston top is decreased. 13,14 Too late an injection, however, can be detrimental to the combustion performance. It raises the local mean equivalence ratio even further, resulting in slower and more fluctuated initial flame propagation.…”

“…11,12 The local equivalence ratio near the spark plug also increases as the distance between the spark plug and the piston top is decreased. 13,14…”

“…It raises the local mean equivalence ratio even further, resulting in slower and more fluctuated initial flame propagation. 14 Priyadarshini et al, 15 observed that when injecting too late, past 50°CA bTDC at 1200 rpm, the fuel is injected into a smaller cylinder volume. The benefits of the bulk flow motion are thus difficult to achieve.…”

Modelling three-way catalytic converter oriented to engine cold-start conditions

“…5–7 Different approaches can be followed to deal with this issue, from using additional hardware components in order to heat up faster the TWC, 8–20 to developing specific control strategies like ignition retardation or homogeneous split mode injection, in order to not only heat up the TWC faster but also reducing HC exhaust raw emissions. 21–23 Ignition retardation allows to delay the combustion process, thereby the combustion remains active even during the exhaust stroke, which helps to speed up the catalyst heating process. Nevertheless, keeping low HC emissions represents a challenge when high levels of ignition retardation are imposed.…”