Operating a compression ignition engine fuelled with a combination of a hydrocarbon fuel and hydrogen

1. A method of operating a compression ignition engine fuelled with a combination of a hydrocarbon fuel and hydrogen and having at least one combustion chamber provided with a glow plug, the method comprising,

during a cold start:

activating the glow plug;

fuelling the engine with the hydrocarbon fuel alone whilst starting;

deactivating the glow plug when a sensed engine temperature reaches a predetermined threshold value which is below a normal engine operating temperature;

after deactivation of the glow plug, implementing a delay prior to commencement of hydrogen supply to the engine, during which the engine continues to be fueled with the hydrocarbon alone;

after the delay, commencing hydrogen supply to the engine; and

progressively increasing the proportion of hydrogen to the hydrocarbon fuel over time as the engine warms up whilst running.

2. The method as claimed in claim 1 , wherein the supply of hydrogen commences after a second threshold value of a sensed engine temperature is reached.

3. The method as claimed in claim 2 , wherein the second threshold value of the sensed engine temperature is less than 60% of a warm running temperature.

4. The method as claimed in claim 3 , wherein the sensed engine temperature is an engine coolant temperature.

5. The method as claimed in claim 2 , wherein after commencement of hydrogen supply, the proportion of hydrogen in the fuel is increased as a function of engine cycles since commencement.

6. The method as claimed in claim 1 , wherein during warm running, hydrogen makes up at least 65% of the fuel's energy content for at least some of the time.

7. The method as claimed in claim 1 , wherein the hydrocarbon fuel is diesel.

8. An electronic control unit for an engine programmed to implement the method as claimed in claim 1 .

9. A computer program product embodied on a computer readable storage medium to cause the engine controller to operate the engine in accordance with claim 1 .

10. A compression ignition internal combustion engine comprising at least one injector for supply of a hydrocarbon fuel to at least one combustion chamber and a hydrogen supply for supplying a controlled quantity of hydrogen to an air intake leading to the combustion chamber, the engine having an electronic controller configured to implement a cold start up process comprising:

activating the glow plug;

fueling the engine with the hydrocarbon fuel alone whilst starting;

deactivating the glow plug when a sensed engine temperature reaches a predetermined threshold value which is below a normal engine operating temperature;

after deactivation of the glow plug, implementing a delay prior to commencement of hydrogen supply to the engine, during which the engine continues to be fueled with the hydrocarbon fuel alone;

after the delay, commencing hydrogen supply to the engine; and

progressively increasing the proportion of hydrogen to the hydrocarbon fuel over time as the engine warms up whilst running.

11. The engine as claimed in claim 10 , wherein the engine is fuelled with the hydrocarbon alone during a cold start, and in which the supply of hydrogen commences after a threshold value of a sensed engine temperature is reached.

12. The engine as claimed in claim 11 , wherein the threshold value of the sensed engine temperature is less than 60% of a warm running temperature.

13. The engine as claimed in claim 11 , wherein after commencement of hydrogen supply, the proportion of hydrogen in the fuel is increased as a function of engine cycles since commencement.

14. The engine as claimed in claim 11 , wherein the electronic controller being configured to cause the glow plug to be activated during engine start-up and deactivated prior to commencement of hydrogen supply.