[AMC-list] LPG/CNG vs. Gasoline

[farna@xxxxxxxxxxx]

Date: Fri, 13 Feb 2015 12:42:09 -0800
From: Jim Blair <carnuck@xxxxxxxxxxx>
To: amc <amc-list@xxxxxxxxxxxx>
Subject: Re: [AMC-list] 4 barrel intake for a 290

I keep hearing that yet the most I see is about 10% difference. Less than
that on a
higher compression engine unless your LPG is cut with Butane. E85 runs
20-30% lower
economy.

From: Ken Ames <ameskg@xxxxxxxxx>
To: "Rambler AMC, Nash, Jeep and family" <amc-list@xxxxxxxxxxxxxxxxx>
Subject: Re: [AMC-list] 4 barrel intake for a 290


But don't you have to use more gallons of LPG compared to gasoline to go
the same
distance?
Or am I thinking of a different fuel?

Ken
==========================================

In a dual fuel configuration you'll burn more LPG than gasoline by volume
to produce the same power/go the same distance. There aren't as many BTUs
in LPG as in the same volume of gasoline. CNG (compressed natural gas) is
a bit more than LPG, but much harder to store and needs a heavier vessel
to carry a comparable amount (of LPG). According to an alternative fuels
chart (http://www.afdc.energy.gov/fuels/fuel_comparison_chart.pdf), 1
gallon of LPG has 73% of the energy of 1 gallon of gasoline, so in the
same engine (dual fuel setup) you should expect to burn ~27% more LPG for
the same power/distance. I've heard it being in the 20-25% range --
depends on vehicle and driving habits as well as load. For ease of math
figure 25% more. LPG is usually cheaper than gasoline, but it has to be at
least 25% cheaper to equal costs. Right now gasoline is at a five year
low, average about $2.20 in the US (national average). LPG is actually a
bit higher at $2.36 (national average) from what I can find. That's for
residential heating, not road fuel, which would be a bit more. Typically
LPG goes down with gasoline since it's a by-product of gasoline, but in
the middle of heating season it's a bit higher due to demand (less demand
for gasoline is driving those prices down... for now!). So at the moment
LPG conversions don't make sense, but that's not likely to last long. For
comparisons, E85 has about the same 20-25% less power as LPG.

You can regain that 20-25% loss on a pure propane (or E85) build. Propane
is 105 octane, E85 is 100-105 (depends on season -- ethanol is reduced to
70-75% in cold winter areas, brought back up to 85% in warm weather).
Since premium gasoline is 93-94, you can build an engine to run at least
one whole point of compression higher -- around 11:1. The problem is you
won't be able to run anything less than premium if you can't find E85, and
that might not even be enough. A pure LPG conversion would have the issue
of being able to find fuel at all. You're not supposed to run heating fuel
as there are no road taxes on it. LPG road fueling stations are few and
far between, and many are only open during regular business hours (9-6 or
so), so you have to carefully plan your driving. TomJ ran his 63 Classic
wagon with 232 on LPG for about 10 years as a pure LPG vehicle. Here's his
conversion info: http://worldpowersystems.com/AMC/LPG/LPG-book-final.html.


Here's a good report with gas mileage on both gasoline and LPG:
https://www.utmb.edu/tstem/tstemutil/Uploads/192013_8_41_29_PM_2037Ansis%20MannieRondina_Propane_Vs_Gasoline_2.pdf


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