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Apparatuses, methods and systems for controlling operation of dual fuel engines are disclosed. One embodiment is a method for controlling operation of a dual fuel engine based upon a combustion index value. The combustion index may be empirically determined to provide desired engine operation at a p

Apparatuses, methods and systems for controlling operation of dual fuel engines are disclosed. One embodiment is a method for controlling operation of a dual fuel engine based upon a combustion index value. The combustion index may be empirically determined to provide desired engine operation at a plurality of ratios of gaseous fuel and liquid fuel. The desired engine operation may include a number of criteria including, for examiner an engine knock criterion and/or an exhaust emissions criterion. The combustion index value may be determined during operation of the engine based upon measured, estimated or predicted engine operating parameters. The combustion index value may be utilized to interpolate between a first engine operating map for a first ratio of gaseous fuel and liquid fuel and a second engine operating map for a second ratio of gaseous fuel and liquid fuel.

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1. A system comprising: an engine structured to selectably combust a combination of liquid fuel injected into a cylinder of the engine and gaseous fuel provided to the cylinder; anda controller configured to control operation of the engine at a plurality of substitution ratios of gaseous fuel for li

1. A system comprising: an engine structured to selectably combust a combination of liquid fuel injected into a cylinder of the engine and gaseous fuel provided to the cylinder; anda controller configured to control operation of the engine at a plurality of substitution ratios of gaseous fuel for liquid fuel by interpolating between a first operating table and a second operating table utilizing a combustion index, the combustion index, the first operating table and the second operating table being stored in a non-transitory controller-readable medium,the first operating table defining first parameters for controlling injection of liquid fuel at a first ratio of substitution of gaseous fuel for liquid fuel,the second operating table defining second parameters for controlling injection of liquid fuel at a second ratio of substitution of gaseous fuel for liquid fuel, the second ratio being greater than the first ratio,the combustion index being empirically determined to provide interpolated liquid fuel injection parameters for a plurality of ratios of liquid fuel and gaseous fuel intermediate the first ratio and the second ratio satisfying an engine knock criterion and an engine emission criterion index. 2. The system of claim 1 wherein the first ratio comprises a minimum gaseous fuel substitution ratio. 3. The system of claim 2 wherein the first ratio comprises 100% liquid fuel. 4. The system of claim 1 wherein the second ratio a maximum gaseous fuel substitution ratio. 5. The system of claim 4 wherein the second ratio comprises at least 90% gaseous fuel. 6. The system of claim 1 wherein the liquid fuel comprises diesel fuel and the gaseous fuel comprises at least one of methane and propane. 7. The system of claim 1, wherein the engine emissions criterion comprises a maximum value for hydrocarbon slip. 8. The system of claim 1, wherein the engine knock criterion comprises a maximum value for occurrences of engine knock. 9. The system of claim 1, wherein the combustion index is determined based on one or more inputs which are distinct from charge lambda. 10. The system of claim 1, wherein the combustion index comprises a plurality of dimensionless values. 11. The system of claim 1 wherein the first operating table and the second operating table specify a pre-injection timing, a pre-injection quantity, a main injection timing, a main injection quantity, a post injection timing, a post injection quantity, and an injection pressure. 12. A method comprising: operating an engine in a first mode in which the engine is fueled with only liquid fuel injected into one or more engine cylinders and the injection of liquid fuel is controlled based upon a first operating map; calculating a combustion index value based upon one or more sensed engine operating parameters and a predetermined formula or a predetermined lookup table;operating the engine in a second mode in which the engine is fueled with a first ratio of substitution of gaseous fuel introduced into an intake system upstream of the one or more engine cylinders for liquid fuel injected into one or more engine cylinders and gaseous fuel introduced into an intake system upstream of the one or more engine cylinders and in which the injection of liquid fuel is controlled based upon a first interpolation between the first operating map and a second operating map, the interpolation being based upon the combustion index value;wherein the predetermined formula or the predetermined lookup table is empirically determined to provide combustion under the one or more sensed operating conditions satisfying an engine knock criterion and an exhaust hydrocarbon criterion for a plurality of ratios of liquid fuel and gaseous fuel substitution of gaseous fuel for liquid fuel. 13. The method of claim 12 further comprising; calculating a second combustion index value based upon one or more second sensed engine operating parameters and the predetermined formula or the predetermined lookup table; operating the engine in a third mode in which the engine is fueled with a second ratio of substitution of gaseous fuel introduced into an intake system upstream of the one or more engine cylinders for liquid fuel injected into one or more engine cylinders and gaseous fuel introduced into an intake system upstream of the one or more engine cylinders, the second ratio being greater than the first ratio, and in which the injection is controlled based upon a second interpolation between the first operating map and the second operating map, the second interpolation being based upon the second combustion index value. 14. The method of claim 12 further comprising operating the engine in a third mode in which the engine is fueled with a second ratio of substitution of gaseous fuel introduced into an intake system upstream of the one or more engine cylinders for liquid fuel injected into one or more engine cylinders and gaseous fuel introduced into an intake system upstream of the one or more engine cylinders and in which the injection is controlled based upon the second operating map. 15. The method of claim 12 wherein the first operating map comprises a set of liquid-fuel-only injection parameters including timings and quantities for pre injection, main injection and post injection. 16. The method of claim 15 wherein the second operating map comprises a second set of injection parameters including timings and quantities for pre injection, main injection and post injection, the second set of injection parameters differing from the set of liquid-fuel-only parameters. 17. The method of claim 16 wherein the second set of injection parameters correspond to a maximum ratio of gaseous fuel to liquid fuel. 18. The method of claim 17 wherein the second set of injection parameters correspond to a ratio of gaseous fuel to liquid fuel of at least 90% gaseous fuel. 19. The method of claim 12 wherein the act of calculating the combustion index value is repeated a plurality of times while the engine is operating. 20. An apparatus comprising: a non-transitory controller readable medium configured to store controller executable instructions configured to generate control commands effective to operate an engine in a first mode in which fueling of the engine consists essentially of liquid fuel injected into one or more engine cylinders and the injection of liquid fuel is controlled based upon a first operating map;determine a dimensionless combustion index value based upon one or more sensed engine operating parameters and a predetermined lookup table or a predetermined calculation;operate the engine in a second mode in which the engine is fueled with a first ratio of substitution of gaseous fuel introduced into an intake system upstream of the one or more engine cylinders for liquid fuel injected into one or more engine cylinders and gaseous fuel introduced into an intake system upstream of the one or more engine cylinders and in which the injection of liquid fuel is controlled based upon a first interpolation between the first operating map and a second operating map, the interpolation being based upon the dimensionless combustion index value;wherein the instructions are configured to generate control commands to operate the engine at a plurality of ratios of substitution of gaseous fuel for liquid fuel. 21. The apparatus of claim 20 wherein the determined dimensionless combustion index value is one of a plurality of values empirically determined to provide combustion satisfying an engine knock limit and an exhaust hydrocarbon limit for a plurality of ratios of substitution of gaseous fuel for liquid fuel and gaseous fuel and a plurality of values of the one or more sensed operating conditions. 22. The apparatus of claim 21 wherein the first operating map comprises a set of liquid-fuel-only injection parameters including timings and quantities for pre injection, main injection and post injection. 23. The apparatus of claim 22 wherein the second operating map comprises a second set of injection parameters including timings and quantities for pre injection, main injection and post injection, the second set of injection parameters differing from the set of liquid-fuel-only parameters. 24. The apparatus of claim 23 wherein the second set of injection parameters correspond to a maximum ratio of gaseous fuel to liquid fuel. 25. The method of claim 24 wherein the second set of injection parameters correspond to a ratio of gaseous fuel to liquid fuel of at least 90% gaseous fuel.