Methods and systems for multi-fuel engine

1. A method, comprising:

adjusting an electric motor output or an engine output to control a speed of a compressor in response to a fuel substitution rate of a multi-fuel engine.

2. The method of claim 1 , wherein the fuel substitution rate is a desired substitution rate, and further comprising adjusting the desired substitution rate in response to a battery state-of-charge being less than a threshold state-of-charge.

3. The method of claim 1 , wherein the fuel substitution rate is a desired substitution rate, and further comprising adjusting the speed of the compressor based at least in part on a desired airflow rate associated with the desired substitution rate.

4. The method of claim 1 , wherein the fuel substitution rate is a desired substitution rate, further comprising determining the desired substitution rate based at least in part on one or more of an engine speed, an engine load, an engine torque, a turbocharger speed, an ambient pressure, an ambient temperature, an intake manifold temperature, and an exhaust manifold pressure.

5. The method of claim 1 , further comprising:

measuring or calculating a fuel substitution rate to determine a current substitution rate; and

comparing the current substitution rate to a desired substitution rate; and

increasing the electric motor output in response to the current substitution rate being less than the desired substitution rate.

6. The method of claim 1 , further comprising:

measuring or calculating a fuel substitution rate to determine a current substitution rate; and

comparing the current substitution rate to a desired substitution rate; and decreasing the electric motor output in response to the current substitution rate being greater than the desired substitution rate.

7. The method of claim 1 , further comprising operating at the desired substitution rate via adjusting an amount of a first fuel injected through a direct injector of an engine and adjusting an amount of a second fuel injected through a port-fuel injector of the engine, wherein the first fuel is different from the second fuel.

8. A system, comprising:

a first fuel system configured to supply a first fuel and coupled to a direct injector positioned to inject directly into a volume of a cylinder of an engine;

a second fuel system configured to supply a second fuel and coupled to a port-fuel injector positioned to inject into an intake port of the cylinder, and the second fuel is different than the first fuel;

a turbocharger having a turbine and a compressor; and

a controller comprising computer-readable instructions stored on non-transitory memory thereof that when executed cause the controller to:

compare a current substitution rate and a desired substitution rate of the first fuel and the second fuel; and

adjust a speed of the turbocharger in response to the current substitution rate not matching the desired substitution rate.

9. The system of claim 8 , wherein the instructions further enable the controller to adjust operation of an electric motor that is coupled to the turbocharger to increase the speed of the turbocharger in response to one or both of: the current substitution rate being less than the desired substitution rate and a current airflow rate being less than a desired airflow rate.

10. The system of claim 8 , wherein the instructions further enable the controller to adjust operation of an electric motor that is coupled to the turbocharger to decrease the speed of the turbocharger in response to one or both of: the current substitution rate being greater than the desired substitution rate and a current airflow rate being greater than a desired airflow rate.

11. The system of claim 8 , wherein the first fuel is a carbon-containing fuel and the second fuel is a carbon-free fuel.

12. The system of claim 8 , wherein the instructions further enable the controller to increase the desired substitution rate in response to a battery state-of-charge being greater than or equal to a threshold state-of-charge.

13. The system of claim 12 , wherein the instructions further enable the controller to decrease the desired substitution rate in response to the battery state-of-charge being less than the threshold state-of-charge.

14. The system of claim 8 , wherein the turbocharger is an electric turbocharger and the electric motor is coupled to the turbine.

15. The system of claim 8 , wherein the first fuel is diesel and the second fuel is hydrogen.

16. A propulsion system for a vehicle, comprising:

an engine comprising a cylinder;

a first fuel system containing a first fuel and coupled to a direct injector positioned to inject directly into a volume of the cylinder;

a second fuel system containing a second fuel and coupled to a port-fuel injector positioned to inject into an intake port of the cylinder, and the second fuel is different than the first;

an electric turbocharger comprising an electric motor, a turbine and a compressor; and

a controller comprising computer-readable instructions stored on non-transitory memory thereof that when executed cause the controller to adjust or maintain a substitution rate of the first fuel relative to the second fuel based at least in part on a highest available rotational speed of the compressor independent of rotational assistance from the electric motor.

17. The engine system of claim 16 , wherein the highest available speed of the compressor with rotational assistance from the electric motor is determined only when a battery state-of-charge is greater than or equal to a threshold state-of-charge.

18. The engine system of claim 17 , wherein the instructions further cause the controller to adjust the desired substitution rate in response to one or more of an engine speed, an engine load, an engine torque, a turbocharger speed, an ambient pressure, an ambient temperature, an intake manifold temperature, and an exhaust manifold pressure when the battery state-of-charge is greater than the threshold state-of-charge.

19. The engine system of claim 16 , wherein the first fuel system is fluidly separated from the second fuel system.

20. The engine system of claim 16 , wherein the instructions further enable the controller to determine a target manifold pressure in response to a desired airflow based on the desired substitution rate, wherein the desired airflow increases as the substitution rate increases.