| CPC F02D 41/3827 (2013.01) [F02D 35/023 (2013.01); F02D 41/0027 (2013.01); F02D 41/401 (2013.01)] | 19 Claims |

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1. A method of operating a gaseous fuelled direct injection diesel cycle internal combustion engine, comprising
introducing a quantity of gaseous fuel directly into a combustion chamber-of said engine, wherein said gaseous fuel comprises at least 60% hydrogen by volume at standard temperature and pressure,
introducing a quantity of pilot fuel directly into said combustion chamber of said engine, such that the quantity of pilot fuel has a pilot energy ratio of less than 1% and greater than 0.26% of a total fuel introduced for at least one engine operating condition; and
igniting said pilot fuel whereby combustion of said pilot fuel triggers the ignition of said gaseous fuel; and said engine maintains good ignition stability of the gaseous fuel for the at least one engine operating condition;
wherein over an entire engine operating map said pilot fuel is on average between 0.26% and 3% of the fuel that is consumed by said engine on an energy basis.
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