Fuelture's installer in Edinburgh, Stenhouse Motor Engineers (SME), warns that direct injection engines cannot undergo LPG conversion. This is because such engines do not have a traditional inlet manifold compared with conventional fuel induction systems.

"For vehicles that do have intake manifolds, they're often too small to accommodate gas injectors," explains SME's Allan Wedgewood. "The problem with trying to feed LPG through petrol injectors is they're liable to melt because the injectors are inside the combustion chamber."

Although direct injection systems are non LPG-friendly, such vehicles are a relatively small proportion of the cars on UK roads. The majority of motorists in the market for LPG will find their car is compatible.

Barry Kenworthy of Nicholson McLaren Engines (NME), Fuelture's technology partner, says that even if liquid LPG could be fed through petrol injectors, the use of such a system would be 'practically and economically impossible'. He says this is because the pressure would have to be increased substantially more than petrol; it would also warrant the use of an extremely costly conversion kit. He adds: "Vehicles fitted with direct injection only include a handful of cars from Mitsubishi, Renault, Citroen, Vauxhall and others.. The minority of direct injection vehicles on the market do not justify the development of a cost-effective and appropriate conversion kit."

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