EXPLAINED: Hi-tech LPG
LPG has long been looked upon as the poor man’s fuel but, in reality, there are many real benefits in running on LPG. It’s cheaper than petrol, so running costs are lower, it’s cleaner and the great thing about today’s hi-tech injection systems is that there is no loss of performance.
The gas revolution began in 2003 when LPG system manufacturers were required to comply with the On Board Diagnostics requirements laid down in Australia’s exhaust emission laws. To comply, they had to be able to isolate the operation of individual cylinders, something that was impossible with the venturi-mixer systems that had been in use since the 1970s.
They also had to be able to isolate individual cylinders to be compatible with other systems on the cars, such as traction control and electronic stability control. Without such control, Ford has not been able to fit its LPG cars with electronic stability control.
The old systems could be made to work on older cars and are still being fitted to older models. But they weren’t suitable for newer cars under the later laws, which was the main motivation for the move to the sequentialinjection systems that are now used.
The main sequential injection system in use injects vapour into the engine in much the same way as sequential petrol injection — the gas is injected through a dedicated LPG injector in the intake port near the intake valve. As a result, the quantity of fuel injected is accurately controlled and, as it is done near the intake valve, the intake manifold isn’t filled with an explosive mixture of air and LPG, which reduces the possibility of a backfire to almost nil.
Holden uses a sequential vapour injection system on its Commodore and Colorado models. When Ford eventually introduces its new dedicated LPG system it will be a sequential liquid-injection one. However, test cars have been on the road for at least five years, which suggests there have been issues with its development.
Fans of liquid injection claim it is more efficient because LPG is injected as a liquid in the same way as petrol. Those who favour vapour injection say it is more accurate and not subject to issues with liquid systems, such as cylinder bore wetting, or refuelling.