DISI INJECTION TIMING STRATEGY

Abstract

A control strategy for a DISI engine fitted with a catalytic converter, for reducing the light off time of the catalyst during cold starts, which comprises setting the ignition timing for each engine cylinder and injecting at least a proportion of the fuel, the timing of the injection in relation to the ignition timing being varied as a function of an engine operating condition.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example only, embodiments of the present invention will now be described with reference to the accompanying drawings wherein:

FIG. 1 is schematic section through a cylinder of a DISI engine;

FIG. 2 is a graph showing cylinder pressure versus crank angle in a DISI engine operated according to a first embodiment of the present invention; and

FIG. 3 is a similar graph showing cylinder pressure in a DISI engine operated according to a second embodiment of the present invention.

Claims

1. A method for reducing light off time of a catalyst coupled downstream of a DISI engine, comprising: setting the ignition timing for each engine cylinder and injecting at least a proportion of the fuel, the timing of the injection in relation to the ignition timing being varied as a function of an engine operating condition.

2. The method as claimed in claim 1, wherein the ignition timing occurs during the expansion stroke.

3. The method as claimed in claim 2, wherein the timing of the injection in relation to the ignition timing is measured from the end of the injection to the spark timing.

4. The method as claimed in claim 3, wherein an initial proportion of fuel is injected prior to a secondary injection.

5. The method as claimed in claim 4, wherein the initial injection of fuel occurs during the intake or compression strokes.

6. The method as claimed in claim 5, wherein the timing of the secondary is injection further a function of any one or more of exhaust gas temperature, engine speed, engine coolant temperature, engine oil temperature, throttle position, ambient air temperature, ambient air pressure, intake air pressure, intake air temperature and compression ratio.

7. A method for reducing light off time of a catalyst coupled downstream of a DISI engine, comprising: injecting fuel and air into each engine cylinder; andretarding ignition timing such that at least a portion of said injected fuel and air exits said engine cylinders unburned thereby raising engine exhaust gas temperature.