Re: IML: propane conversions to an imperial

[dardal@xxxxxxxxxxxxxxx]

Mike, good input for our European friends that are trying to save fuel cost. 
Here are some clarifications.

Quoting mike sutton <mikanlin62@xxxxxxxxxx>:

 
> to and while the octane content is higher the btu values are lower than 
> gasoline.
....
>  Higher compression is a must if you want to regain the power loss from the 
> lower btu value of the fuel , and depending on the year of the engine you 
> can shave the cylinder heads ,....

While its true, that propane has lower energy per unit mass (and unit volume in
the liquid state), this is not the reason of lost power at WOT (Wide open
Throttle).  It is nevertheless the reason of reduced range for the same fuel
capacity (which is hard by the way to match the stock gasoline fuel capacity
with propane due to the bulky shape of the fuel tanks, and that's why most
conversions retain the stock gasoline system).

The reason of lost performance (for both propane and natural gas) is the
following.  As we all know, the maximum torque of a spark ignition engine is
limited by how much air (oxygen) can be sucked into the cylinders.  When you
use gaseous fuel, the fuel itself will ocupy a certain amount of volume in the
cylinders, which means that certain amount of air is displaced (when running on
gasoine, the fuel is liquid [droplets] which occupies a minute amount of
volume).  Therefore, the power los is due to volumetric efficiency loss (the
torque loss is of the order of 10%).  For this reason, the extra torque that
you can gain by raising the compression ratio will never match the lost torque
due to volumetric efficiency.  Also, given that the range of the vehicle will
always be lower on propane, that means you may have to maintain the gasoline
system, which rules out increased compression ratio.

I was involved in a propane conversion designed to exactly attack this problem,
the loss of power of the propane conversion.  The idea was to inject the
propane in the liquid state in the intake manifold (like a normal port
injection gasoline car), and let the rapidly expanding propane suck the heat
for evaporation out of the air charge as opposed from the coolant, as Mike
described.  The result is, that the cooling effect increases volumetric
efficiency, and the gained torque more than compensates for the loss due to the
gaseous fuel.  During the mid nineties, Chrysler of Canada had developed this
conversion for van fleets, but there were always problems with the in-tank pump
(necessary) which was pumping propane in its saturation state (i.e.,
"boiling").

Incidentally, I had read an interesting SAE paper from the 60's that suggested
the same idea, but applied to carburated vehicles without electronics.  They
had suggested for the propane to be injected inside a heat exchanger, which
will be then inserted inside a large air-box.  The engine sucked its air
through that air box, so the engine got its chilled air while the propane
sucked the heat of evaporization also from that same cooling air.  In theory,
the effect is the same as above, but the hardware will have to be designed
carefully to not add excessive restrictions to the intake air.  Such a
conversion could prove beneficial for performance, fuel economy, and exhaust
valve life for older cars, such as Imperials.

Now, for all our vendors out there, building such a system for Imperials would
make you some good profit!

D^2



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