Method of operating an internal combustion engine with direct fuel injection
In a method of operating a spark ignition internal combustion engine with direct fuel injection wherein combustion air is supplied to a combustion chamber, fuel is injected into the combustion air during an intake stroke via a fuel injector in a pilot injection using a first fuel quantity so as to from a homogeneous lean air/fuel mixture in substantially the entire combustion chamber, in a main injection subsequently a second fuel quantity is injected in multiple injection steps just before ignition time so as to form a stratified rich air/fuel mixture in the area of a spark plug and the stratified fuel charge is then ignited 2° CA to 10° CA after completion of the injection of the main stratified injection.
1. A method of operating a spark-ignition internal combustion engine ( 10 ) with direct fuel injection, comprising the steps of:
supplying a combustion chamber ( 18 ) with combustion air;
injecting, in a pilot injection, a first fuel quantity into the combustion chamber ( 18 ) during an intake stroke of the internal combustion engine ( 10 ) so as to form with said pilot injection (M H ) a homogeneous, lean air/fuel mixture (λ>1) in substantially the entire combustion chamber ( 18 );
injecting subsequently, in a main injection (M S ), a second fuel quantity in into the combustion chamber ( 18 ) directly before the ignition time (ZT) such that said main injection (M S ) forms a stratified, rich air/fuel mixture (λ<1) in the region of the spark plug ( 26 ), and
igniting the air/fuel mixture by means of a spark plug ( 26 ) at a predetermined ignition time (ZT),
said main injection (M S ) being carried out as a multiple injection with a plurality of stratified injections in rapid succession, the end of the first stratified injection of the main injection (M S ) occurring at approximately 2° CA to 10° CA before the ignition time (ZT).
2. The method as claimed in claim 1 , wherein the main injection (M S ) is carried out as a double injection with two stratified injections, and the ignition time (ZT) occurs at one of the points in time; after the second stratified injection of the main injection and between the first and second stratified injections of the main injection.
3. The method as claimed in claim 1 , wherein the main injection (M S ) is carried out as a triple injection with three stratified injections, and the ignition time (ZT) occurs one of the points in time; after the third-stratified injection of the main injection and between the first and second, or between the second and third, stratified injections of the main injection.
4. The method as claimed in claim 1 , wherein, in the case of operation with high residual exhaust gas rates, the pilot injection (M H ) generates a slightly lean air/fuel mixture of λ≈1.3, in the combustion chamber ( 18 ).
5. The method as claimed in claim 1 , wherein, averaged across the entire combustion chamber ( 18 ), the air/fuel mixture after the second, stratified injection (M S ) is approximately stoichiometric (λ≈1).
6. The method as claimed in claim 1 , wherein the ignition time (ZT) occurs between 0° CA and approximately 35° CA before top dead center (ITDC).
7. The method as claimed in claim 1 , wherein also the pilot injection (M H ) is carried out as a multiple injection with a plurality of homogeneous individual injections.