EX­PLAINED: Hi-tech LPG

Herald Sun - Motoring - - Ask Smithy -

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.

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