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Thread: LPG? probably a question for for Nene!

  1. #1
    Guest sparkyhx's Avatar
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    LPG? probably a question for for Nene!

    Bit of a techy question but

    given that LPG has an 'octane' equivalent of 112 and genarates higher combustion temps. Surely this means it more efficient?

    why is it that LPG fuel economy is 10-20% less than petrol?

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    Simple really, because it is a gas and not a liquid so there for it is less dense per volume when compared to petrol, hence why it is not as efficient, I know there has been some work to try and get liquid injection systems but the are a bit off yet.

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    Bod Jon's Avatar
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    There is more chemical energy in one litre of petrol, than there is in one litre of LPG, so you need more litres to achieve the same thing (assuming they're equally efficient).

    LPG's octane level does allow slightly advanced ignition timing and boost level, so the difference is reduced a little.
    Last edited by Jon; 18-06-2009 at 17:35. Reason: speeling

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    Bod Jon's Avatar
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    Quote Originally Posted by Wikipedia
    LPG has a typical specific calorific value of 46.1 MJ/kg compared to 42.5 MJ/kg for diesel and 43.5 MJ/kg for premium grade petrol (gasoline). However, its energy density per unit volume is lower than either petrol or diesel.
    A litre of petrol weighs about 720 grams, but a litre of LPG will vary depending on the pressure it's stored at, so it's tricky to compare figures really.

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    Guest clai cerrig's Avatar
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    I don`t care its still £0.479 per Liter here against Petrol

    When i was running the s14 @stage 2 it worked out at between 4 and 7 miles to the gallon less depending on my right foot

    And last weekend running the Jeep (V8 4.7Ltr) i got just on 15.3 mpg @ 0.49p litre compared to petrol 21.6 mpg @ £1.02 litre going to Donnington then Apex and Home to Anglesey

    Also ask Kev (SM) he kept a rather imressive spread sheet with all his running costs on

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    Guest sparkyhx's Avatar
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    Quote Originally Posted by clai cerrig View Post
    I don`t care its still £0.479 per Liter here against Petrol

    When i was running the s14 @stage 2 it worked out at between 4 and 7 miles to the gallon less depending on my right foot

    And last weekend running the Jeep (V8 4.7Ltr) i got just on 15.3 mpg @ 0.49p litre compared to petrol 21.6 mpg @ £1.02 litre going to Donnington then Apex and Home to Anglesey

    Also ask Kev (SM) he kept a rather imressive spread sheet with all his running costs on
    I'm currently building a spreadsheet - so far I have averaged just over 30mpg 'equivalent' on my Lexus, with predominantly town driving. I am expecting to see close to 50mpg equivalent on a total LPG run on motorways. Not bad for a 4.3L V8 barge
    Thats taking into account the Petrol I put in as well.
    Last edited by sparkyhx; 18-06-2009 at 19:54.

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