Propane (or a mixture of propane and butane called Handigas or Easigas) does not have the same properties as diesel. Diesel has a tendency to "knock" or rather ignite by itself due to a pressure rise - therefore no sparkplugs are found on a diesel engine. Furthermore, propane has similar properties as petrol, resisting self ignition and will thus be more suitable in a petrol engine than in a diesel engine. In fact, I have come accross a business that converts a normal petrol vehicle to a Handigas vehicle: the Handigas is controlled via a flow controller, routing it through the air cleaner and carburettor to the inlet manifold (retaining it). The only significant adjustment is retarding the ignition (because the Handigas has a tendency to "knock" / self ignite quicker than petrol).
I thought you had to retard the ignition on a propane engine because the flame speed is faster in the propane, probably due to not having to evaporate the liquid fuel droplets. This has nothing to do with self ignition.
In this case, Greg, your pretty much right on. In some cases, such as our fork lift (lift truck) we switch back and forth from gasoline to propane with no timing changes at all (it was originally set up for gasoline). Just have to wait a few seconds for the gasoline in the float bowl to be used up when switching to propane, it seems to go rather quickly when switching back to gasoline??? Power is down a bit on propane, latent energy content or some such, not timing.
One obvious reason for the power dropping is that air volume is being taken up by gas, but I don't think that's a huge effect. Oh, I've just been told the air fuel ratio is 15.6, so you'd expect 6% less air, hence power, at lambda=1.
Thru the years we converted many fork lift engines from gasoline to LPgas. The only changes were the carburators, plus hoses and tanks. Some units were done to use gasoline or LPgas and used a plate between the carb. and manifold which fed the LPgas when switched from gasoline. The main reason for the LPgas is cleaner emmissions and extended engine life as there is no liquid gasoline to wash lubrication out. Oil never gets dirty but has to be changed by hours of use. However, forklifts do not use the range of rpm that a car would use and are limited to much slower speeds. No adjustments were needed to timing, plug gap, etc.
I have to agree about not converting a diesel, as the ignition system of a diesel is compression and proper timed injection and I don't beleive LP could be set up to work this way.
Good luck.
Ed Kay Ed Kay
Well, boys and girls. If you wish to see a practical application of propane in diesel engines, just have a peek at the Euro truck racing scene. Sure, they blow rather often, but, man are they FAST. The rules require that they have a fifth wheel capable of pulling a trailer, but that's about all.
I have worked extensively with propane both as a replacement fuel for gasoline, and as a potential replacement fuel for diesel.
Propane has an octane rating of 104 (depending on its purity, amount of propylene and ethane, and its origination), has a slightly slower flame travel speed than gasoline, a critical compression ratio of about 13:1, and runs at Stoich of 15.5. Its lean and rich limits are 2.1 to 9.6%. Its ideal operating range is around 6.5% (at Stoich). Its combustion flame temperature is around 3500 deg F.
Evelrod is right about using propane as a power booster for trucks, just ask several vendors marketing the kits now, they have never been so busy! But then, so have diesel engine mechanics, as there have been numerous failures. Some dealerships are instructing employees to look for signs of an installed or recently removed propane fumigation system, and if found, the engine warranty is voided! One interesting item I have noted, this problem is regional, and seems to be more pronounced in the midwest and deep south, possibly due to the concentration of diesel ¾ and 1 ton trucks.
Once propane to diesel replacement exceeds about 15%, the combustion pressures exceed the physical limitation of many engines (when combined with diesel) and can cause pistons to destruct, cracked valves and heads, to burned turbo bearings and seals, and warped exhaust manifolds!
Propane as a fumigation fuel with diesel has its place, but in very small minor fractions of less than 10%, and be knock limited, with exhaust thermocouples monitoring temps.
Can someone please tell me the ideal compression ratio and stoiciometric mixture of propane please! I am undertaking a project which involves converting a two stroke petrol engine to run on propane. any help appreciated
Propane works well with a compression ratio of around 10:1, despite what is thought about its octane (104). Since propane is metered in as a dry vapor, there are no evaporative cooling effects that could lower combustion temperatures and allow compression ratios in the 12-13's. The critical compression ratio is around 13:1. The Stoich ratio is 15.5. Please note that this is with US grade propane with a fuel standard of HD-5, or no less than 90% propane and no more than 5% ethane. Other parts of the world allow propane/butane blends from 40/60 to 60/40%.
One last thing, the heavier the duty cycle will be (running at 75% of engine rating) the lower the compression ratio should be.
Regards;
Years ago a company in Calgary Alberta ran propane into the air inlet of some class 8 (heavy) truck diesel engines but I do not know what the long term results where. Only that it was done and did work hauling heavy loads in steep mountain country. As I recall it was done with the enginge manufacturer. There is currently a company called Westport Systems who have a Cummins diesel running on natural gas (I know for sure as he passed me on the freeway with signs all over the trailer) but I don't know if they are running blended with diesel or on straight natural gas. They may have a web sight.
The Westport Cummins is a dedicated Natural Gas engine application. It is not a dual fuel engine. It has shown some good results and may be one of the cleanest large engines running.
There is information on the web about the engine, but its mostly marketing material.
