Max compression ratio for propane
Max compression ratio for propane
(OP)
A question was asked of me regarding the maximum compression ration for a propane fueled engine.
I believe it to be 13 or 14:1. Anyway just hoping some one can help.
thanks
Gord
I believe it to be 13 or 14:1. Anyway just hoping some one can help.
thanks
Gord





RE: Max compression ratio for propane
RE: Max compression ratio for propane
Max compression ratio will depend on many things including camshaft timing.
www.retallickeng.com.au
Was told it couldnt be done, so
i went and did it!
RE: Max compression ratio for propane
Regards
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RE: Max compression ratio for propane
Introduced as a carburated-gas, propane provides no evaporative charge cooling, and therefore running richer than stoichiometric further does not provide any further cooling benefit.
There are systems out that inject propane as pressurized-liquid directly into the inlet tract, and these do provide significant charge cooling like gasoline. However, these systems are the exception rather than the rule of most aftermarket propane conversions, which pre-expand the propane before admitting it into the intake as a gas.
In summary, the tolerance for increased compression ratio in a converted propane engine is relatively benign compared to the baseline gasoline engine. The exception is a system that injects propane as liquid in the intake; there you can easily increase the CR by 1 or 2 full points if everything else is equal.
RE: Max compression ratio for propane
RE: Max compression ratio for propane
RE: Max compression ratio for propane
Anbody know where Glen Sali of propane drag car era is these days?,
Thanks again
Gord
RE: Max compression ratio for propane
methane propane iso-octane
RON 120 112 100
MON 120 97 100
Heat of Vaporisation (MJ/kg) 0.5094 0.4253 0.2712
Net Heating Value (MJ/kg) 50.0 46.2 44.2
Vapour Pressure @ 38C ( kPa ) - - 11.8
Flame Temperature ( C ) 1950 1925 1980
Stoich. Flame Speed. ( m/s ) 0.45 0.45 0.31
Minimum Ignition Energy ( mJ ) 0.30 0.26 -
Lower Flammable Limit ( vol% ) 5.0 2.1 0.95
Upper Flammable Limit ( vol% ) 15.0 9.5 6.0
Autoignition Temperature ( C ) 540 - 630 450 415
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RE: Max compression ratio for propane
Common logic would dictate that a fuel with an octane rating of 100 would work best in an engine with about 11:1, but here we go with race engines running 14:1, and they are making lots of power. A friend of mine is a mud racer (big engine, little truck, 4 wheel drive) running a 540 CID with 14:1, on alcohol. Another friend is a local drag racer and on 104 octane racing fuel, he chooses 13:1.
Most engines use a lower compression ratio for emission controls and engine longevity. My lawn mower engine uses 7:1 as an example, and it runs, and runs, and runs, longer than I would care to admit, with minimal maintenance.
When we work on the engine in a dyno cell and are setting the initial timing curve, we work on a best torque limited curve, before detonation. Increased compression will usually require a lower total advance and less agressive curve before detonation, at best torque.
Propane behaves like the other fuels, but as mentioned, since it is a dry fuel with practically no heat absorbtion or charge cooling. When we have detonation from compression, reducing ignition timing will have little effect.
On a valve-in-block engine, one can tolerate higher compression ratio than a modern valve in head engine, due to a less efficient combustion process. In this case, its the engine, not the fuel that is dicatated by compression.
Personally, on propane, in a modern engine since the early 1990's, 10:1 is a good starting place, balancing engine longevity and power. 11:1 would give a little more power but the fuel mixtures and timing will have to be monitored more closely, and 12:1 needs constant vigilance on the above.
Franz
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RE: Max compression ratio for propane
RE: Max compression ratio for propane
Question to ponder:
Does a diesel engine run on a constant detonation mode?
Franz
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RE: Max compression ratio for propane
I'm thinking those propane-injection power adders are sending peak cylinder pressure sky high.
For what it's worth, diesel engines seem to be moving towards a combustion system with more pre-mixed combustion (possibly entirely pre-mixed in the low-load regime), but with the rate of heat release (and peak cylinder temperature, hence NOx emissions) controlled by using extremely high EGR in these part-load conditions.
I somehow doubt that the propane power-adder folks are putting that much research into how the combustion is progressing.
RE: Max compression ratio for propane
Gord
RE: Max compression ratio for propane
If liquid state propane is introduced to the engine, there is change of state heat of evaporation required to vaporize the liquid, and then also roughly isenthalpic expansion which gives further charge densification. Per the Classius-Clapeyron relationship propane will have less cooling than larger molecular weight fuel.
I am guessing that the LP is vaporized prior to carburator so much of the cooling advantage is lost.
RE: Max compression ratio for propane
The rule of thumb for home racing was 12.5 : 1 compression on Aviation gas at 105 Octane. My present car has 11.5 to 1 and requires 91 to 93 (depending on altitute). But it has more bells and whistle than you can believe. Thats how I got to 11 to 1 with you every day vehicle.
RE: Max compression ratio for propane
so it's 13 to one in a street and strip trailer towing package..
works just fine, no detonation
cleanburner