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In one example, a system for a vehicle travelling on a surface is described. The system includes an engine with a cylinder. The cylinder includes a fuel injector that is supplied with gaseous fuel and liquid fuel by a fuel delivery system. The fuel injector is mounted in the vehicle such that the fu

In one example, a system for a vehicle travelling on a surface is described. The system includes an engine with a cylinder. The cylinder includes a fuel injector that is supplied with gaseous fuel and liquid fuel by a fuel delivery system. The fuel injector is mounted in the vehicle such that the fuel injector inlet faces at least partially toward the road surface. The orientation of the fuel injector enables a quick transition from liquid fuel to gaseous fuel because the gaseous fuel can rise to the injectors and be preferentially injected. Further, various approaches are described from transitioning operation between gaseous and liquid fuel injection.

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1. A method of controlling an engine having a cylinder, the cylinder having a first, direct, fuel injector and a second fuel injector, the second fuel injector selectively supplied with one or more of gaseous fuel and liquid fuel by a fuel delivery system, the first, direct, fuel injector supplied w

1. A method of controlling an engine having a cylinder, the cylinder having a first, direct, fuel injector and a second fuel injector, the second fuel injector selectively supplied with one or more of gaseous fuel and liquid fuel by a fuel delivery system, the first, direct, fuel injector supplied with liquid fuel, the method comprising: delivering liquid fuel to the first, direct, injector of the cylinder;selectively delivering liquid fuel to the second injector of the cylinder during a first condition;selectively delivering gaseous fuel to the second injector of the cylinder during a second condition, the second condition different than the first condition; andadjusting injection of the first injector when transitioning the second injector from liquid fuel to gaseous fuel and when transitioning the second injector from gaseous fuel to liquid fuel. 2. The method of claim 1, wherein the first condition includes when an operator requests liquid fuel, when gaseous fuel pressure is below a threshold, or when there is heavy engine loading; and wherein, the second condition includes when the operator requests gaseous fuel or when liquid fuel storage level is below a threshold. 3. The method of claim 1, wherein the adjusting injection of the first injector when transitioning the second injector from liquid fuel to gaseous fuel includes increasing injection of the first injector when ceasing injection on the second injector, such that the amount of power generated by the engine is maintained in the transition. 4. The method of claim 3, wherein the adjusting injection of the first injector when transitioning the second injector from liquid fuel to gaseous fuel includes decreasing injection of the first injector when resuming injection on the second injector, such that the amount of power generated by the engine is maintained in the transition. 5. The method of claim 1, wherein the adjusting injection of the first injector when transitioning the second injector from gaseous fuel to liquid fuel includes increasing injection of the first injector when ceasing injection on the second injector, such that the amount of power generated by the engine is maintained in the transition. 6. The method of claim 5, wherein the adjusting injection of the first injector when transitioning the second injector from gaseous fuel to liquid fuel includes decreasing injection of the first injector when resuming injection on the second injector, such that the amount of power generated by the engine is maintained in the transition. 7. The method of claim 1, further comprising: adjusting injection of the first injector and the second injector in response to knock. 8. The method of claim 7, wherein the adjusting injection of the first injector includes increasing injection of the first injector and the adjusting injection of the second injector includes decreasing injection of the second injector when liquid fuel is delivered to the first and second injectors. 9. The method of claim 8, further comprising: transitioning from delivering liquid fuel to delivering gaseous fuel to the second injector when injection of the first injector is above a threshold and when knocking conditions are present. 10. The method of claim 4, wherein transitioning from delivering liquid fuel to delivering gaseous fuel to the second injector includes ceasing injection of the second injector; stopping delivery of liquid fuel by the fuel delivery system;starting delivery of gaseous fuel by the fuel delivery system;purging the second injector of gaseous fuel; andresuming injection of the second injector. 11. The method of claim 10, further comprising disabling a liquid fuel pump associated with the fuel delivery system to stop delivery of the liquid fuel by the fuel delivery system. 12. The method of claim 10, further comprising opening a gaseous fuel valve associated with the fuel delivery system to start delivery of the gaseous fuel by the fuel delivery system. 13. The method of claim 6, wherein transitioning from delivering gaseous fuel to delivering liquid fuel to the second injector includes: ceasing injection of the second injector;stopping delivery of gaseous fuel by the fuel delivery system;starting delivery of liquid fuel by the fuel delivery system;purging the second injector of liquid fuel; andresuming injection of the second injector. 14. The method of claim 13, further comprising closing a gaseous fuel valve associated with the fuel delivery system to stop delivery of the gaseous fuel by the fuel delivery system. 15. The method of claim 13, further comprising starting a liquid fuel pump associated with the fuel delivery system to start delivery of the liquid fuel by the fuel delivery system. 16. The method of claim 1, further comprising: monitoring fuel rail pressure to determine when gaseous fuel has been purged from the fuel rail, and applying high pressure gaseous fuel to purge liquid fuel from the fuel rail while delivering gaseous fuel to the fuel rail. 17. A method of controlling an engine having a cylinder, the cylinder having a first, direct, fuel injector and a second fuel injector, the second fuel injector selectively supplied with one or more of gaseous fuel and liquid fuel by a fuel delivery system, the first, direct, fuel injector supplied with liquid fuel, the method comprising: delivering liquid fuel to the first, direct, injector of the cylinder;selectively delivering liquid fuel to the second injector of the cylinder during a first condition;selectively delivering gaseous fuel to the second injector of the cylinder during a second condition, the second condition different than the first condition;increasing injection of the first injector and ceasing injection of the second injector when transitioning the second injector from liquid fuel to gaseous fuel and when transitioning the second injector from gaseous fuel to liquid fuel; anddecreasing injection of the first injector when resuming injection of the second injector.