Methods and systems for compression ignition in a multi fuel engine

1. A method for an engine, comprising:

injecting hydrogen as fuel to one or more engine cylinders via a corresponding direct fuel injector coupled to each of the one or more engine cylinders that is spaced away from an intake valve of the respective one or more engine cylinders;

compression igniting the injected hydrogen;

during injecting only hydrogen to the one or more engine cylinders, supplying an amount of exhaust gas recirculation (EGR) to each of the one or more engine cylinders through an EGR passage that is in fluidic communication with one or more intake valves of the one or more engine cylinders and one or more exhaust valves of the one or more engine cylinders, the amount of EGR mixing with the hydrogen within each of the one or more engine cylinders;

wherein the amount of EGR is adjusted based on the amount of hydrogen injected into the one or more engine cylinders;

continue injecting only hydrogen to the one or more engine cylinders via the corresponding direct fuel injector coupled to each of the one or more engine cylinders for a pre-calibrated number of engine cycles; then

responsive to injecting only hydrogen to the one or more engine cylinders via the corresponding direct fuel injector coupled to each of the one or more engine cylinders for the pre-calibrated number of engine cycles, inject a liquid fuel from the same corresponding direct fuel injectors that previously injected only hydrogen.

2. The method of claim 1 , wherein the fuel injected is only hydrogen, the method further comprising, adjusting an amount of hydrogen injected in an engine cycle based on one or more of a torque demand, an engine speed, and an engine temperature.

3. The method of claim 2 , wherein for each engine cycle, a first portion of the amount of hydrogen injected every engine cycle is injected first and then a second, remaining portion of the amount of hydrogen injected every engine cycle is injected.

4. The method of claim 3 , wherein the corresponding direct fuel injector is a high pressure direct injector, wherein for each cylinder of the one or more engine cylinders, the injections of the first portion of the amount of hydrogen injected and the second portion of the amount of hydrogen injected are carried out via the high pressure direct injector coupled to each cylinder.

5. The method of claim 4 , further comprising, upon injecting only hydrogen from the high pressure direct injector for a threshold number of engine cycles, injecting a different, liquid fuel from the high pressure direct injector for a first number of engine cycles.

6. The method of claim 5 , wherein the different, liquid fuel is diesel.

7. The method of claim 1 , wherein the liquid fuel is diesel, and wherein the pre-calibrated number of engine cycles corresponds to each injector's propensity for loss of lubrication.

8. The method of claim 1 , wherein the amount of EGR is further adjusted based on one or more of engine load and the engine speed.

9. The method of claim 1 , further comprising, during an engine start, injecting each of diesel and hydrogen as fuel to the one or more engine cylinders, and in response to the engine temperature increasing to above a threshold temperature, switching to injecting only hydrogen to the one or more engine cylinders.

10. A method for a multi-fuel engine, comprising:

during a first condition, injecting a mixture of diesel and hydrogen to a cylinder of the engine in at least one stroke of a four stroke combustion cycle and compression igniting the mixture;

during a second condition,

injecting only hydrogen to the cylinder of the engine in at least one stroke of a four stroke combustion cycle and compression igniting the hydrogen, and continue injecting only hydrogen to the cylinder via a direct fuel injector coupled to the cylinder for a pre-calibrated number of engine cycles,

then responsive to injecting only hydrogen to the cylinder via the direct fuel injector for the pre-calibrated number of engine cycles, inject a liquid fuel from the same direct fuel injector that previously injected only hydrogen; and

during the second condition, supplying an amount of exhaust gas recirculation (EGR) to the cylinder;

wherein the amount of EGR is adjusted based on the amount of hydrogen injected into the cylinder.

11. The method of claim 10 , wherein the first condition includes an engine temperature being lower than a threshold engine temperature and the second condition includes the engine temperature being higher than the threshold engine temperature and a level of hydrogen in a fuel reservoir being higher than a threshold level.

12. The method of claim 10 , wherein the direct fuel injector is a high pressure direct injector coupled to the cylinder.

13. The method of claim 10 , wherein during the second condition, for each engine cycle, the hydrogen is injected in two or more batches.

14. The method of claim 11 , wherein the amount of EGR is adjusted based on one or more of an engine load and an engine speed.

15. The method of claim 14 , wherein during the first condition, adjusting a ratio of hydrogen to diesel based on one or more of a torque demand, the engine speed, the engine temperature, and the level of hydrogen in the fuel reservoir.

16. The method of claim 10 , further comprising, during the second condition, suspending injection of hydrogen and injecting diesel through the direct fuel injector for one or more engine cycles.

17. The method of claim 10 , further comprising, during the second condition, switching from injecting only hydrogen to the cylinder to injecting one of the mixture of diesel and hydrogen, and only diesel in response to increase in torque demand to above a threshold demand.

18. A system for an engine, comprising:

a controller storing instructions in non-transitory memory that, when executed, cause the controller to:

during an engine start, operate the engine by combusting only diesel in each engine cylinder of the engine using a four-stroke cycle, wherein the engine comprises multiple engine cylinders;

in response to an engine temperature increasing to above a threshold temperature, switch to operating the engine by combusting only hydrogen in each cylinder of the engine using a four-stroke cycle; and

continue injecting only hydrogen to each cylinder of the engine via a corresponding direct fuel injector coupled to each cylinder of the engine for a pre-calibrated number of engine cycles; then

responsive to injecting only hydrogen to each cylinder via the corresponding direct fuel injector for the pre-calibrated number of engine cycles, inject a liquid fuel from the same corresponding direct fuel injectors that previously injected only hydrogen to lubricate the corresponding direct fuel injectors, wherein the liquid fuel is diesel, and wherein the pre-calibrated number of engine cycles corresponds to each injector's propensity for loss of lubrication.

19. The system of claim 18 , wherein each of the diesel and the hydrogen is direct injected to each cylinder of the engine under high pressure, and compression ignited without spark.

20. The system of claim 18 , wherein the controller includes further instructions to: during injecting only hydrogen to each cylinder, supply an amount of exhaust gas recirculation (EGR) to each cylinder, the amount of EGR mixing with the hydrogen within each cylinder, wherein the amount of EGR is adjusted based on the amount of hydrogen injected into each cylinder.