Split cycle engine and method of operation

A method of operating an engine on gaseous fuel, comprising the steps of:

• adjusting the concentration of the gaseous fuel to a level such that the fuel can be compressed at a ratio of at least 10:1 to 16:1 without predetonating, compressing the gaseous fuel in a first compression chamber having a compression ratio of at least 10:1 to 16:1, compressing air in a second compression chamber, mixing compressed air from the second compression chamber with compressed fuel from the first compression chamber to dilute the gaseous fuel to a level of concentration at which the fuel can burn and expand in a combustion chamber, and delivering expanding gases from the combustion chamber to an expansion chamber to drive an output member in the expansion chamber.

A split cycle engine for burning gaseous fuel, comprising:

• a first compression chamber of variable volume, a fuel line through which the gaseous fuel is delivered to the first compression chamber, air inlets spaced apart along the line for introducing air into the line to progressively decrease the concentration of the gaseous fuel as it passes through the line, a blower in the line for increasing the pressure and amount of fuel delivered to the first compression chamber, a second compression chamber for compressing air, a blower for increasing the pressure and amount of air delivered to the second compression chamber, a combustion chamber in which compressed fuel and air from the compression chambers are combined to further reduce the concentration of the fuel to a level at which the fuel can burn and expand, and an expansion chamber having an output member which is driven by expanding gas from the combustion chamber.