There's been quite a few posts on LPG in the forums for individual models but a lot of info. is the same regardless of model. I was going to start another thread in 'General' just on LPG but at the risk of hijacking your thread Heeno, might start with a post here.
Federal govt. $1000 rebate: was to have been introduced in 2011 to offset the effect of the introduction of excise on LPG. May be brought forward sooner.
State Govt. $1000 rebate: I think that WA at least, also offers a $1000 rebate. Not sure what happens if Fed. rebate comes in. Could end up being paid for converting
.
Excise: Currently no federal excise on LPG. Was to have been introduced in 2008, ramping up at 2.5 c/l/yr to a level corresponding to the energy content of LPG relative to petrol:38c/l); LPG: ~25c/l ? The LPG and Taxi industries complained and it was changed to starting 2011 going to 2015, still 2.5c/l/yr, going to 12.5c/l. Not sure whether excise will change if rebate is brought forward - I might be being cynical but Govts tend to do such things and then shout about the benefit only.
Fuel consumption: LPG contains less energy per litre than petrol - fuel economy will be about 30% greater on a volume basis on LPG vs petrol.
Economics: There is an opportunity cost associated with the cost of conversion - how much could be earnt on the money spent on the cost of conversion? Will a car with LPG be worth more, less or the same as one without - ie. do you write the entire cost on conversion off vs the savings, or more, or less? Dedicated gas engine oils cost a little bit more.
Security: For VN Calais on, does the LPG system bypass the factory anti-theft system (effectively fuel cut with fixed spark timing only)? Will cars be stolen for their gas equipment?
Factory systems may include uprated rear springs to cater for the heavy tank in the boot, which could be 70-80kg when full.
Because LPG is introduced as a vapour, the inlet valves, valve guides and cylinders are not cooled by the fuel, so run hotter, which may cause them to fail earlier than on petrol. If the engine coolant hoses are tapped into the inlet manifold rather than the heater circuit, some of the heat of evaporation of the LPG can be used to reduce the cylinder head temp. a bit. Dedicated gas oils should be used because the higher temperatures generated increase the formation of acids which end up in the oil. The gas oils are buffered (pH ~constant) to protect the engine. The gas oils can be higher viscosity at higher temperature too; like 20W/60 in place of 20W/50.
Octane: The Australian fuel standard for Autogas requires a minimum octane rating of 90.5 RON, which is slightly higher than that required for standard unleaded and a bit less than that for premium unleaded. Some individual fuel companies will guarantee that their gas is higher octane than the minimum. (If you live away from a capital city, you might be getting a higher octane because the same LPG tanker truck also services the BBQ bottle supply, which must be pure propane, or close to it).
Power loss: Not noticeable during normal driving in my experience, unless the conversion is really poor. The LPG, introduced as a gas, displaces some of the air in the manifold/cylinder and heating of the air, where it's not cooled by the evaporation of (some of) the fuel, reduces the mass of air in the cylinders some more. ~5% loss
at wide open throttle. Some conversions, especially older types, can place restrictions in the air intake path.
Ignition timing for LPG and petrol will be similar but it depends on the engine.
Feel good stuff (or not): LPG produces less CO2 for a given amount of energy than does petrol. NOx, which are also greenhouse gases (about 20X more effective (worse) than CO2), are generally higher with LPG, because combustion chamber temperatures are hotter than with petrol. LPG is generally sourced locally, hence
may help the economy. Unlike ethanol or biodiesel, LPG is no more renewable than other petroleum based fuels; when the oil and gas run out, so does LPG (but thats a few years away yet ).
