Has anyone heard of these propane kits? I hear that these kits let you use little amounts of propane to incerase power, and fuel eficiency. I heard someone use it for a mercedes 300D, and that it increased the power to abut 200HP! Is propane dangerous for diesel engines? I thought about finding a kit for my 2006 Freightliner Columbia semi truck. I need it to help me drive up steep hills easier. I think it's a pretty cool idea. Does anyone know more about them?

I have heard of propane injection, a long time ago, never looked very much into it. My understanding is that it is hard on them as it is a good way to freeze and shatter pistons if not very carefully watched and used in short minor amounts.

Propane is just a second fuel. There is nothing magical about it.

The exact same effect can be had by turning up your maximum fuel delivery (Turning up the pump).

The reason people see higher MPG is, again, propane is a second fuel. Diesels only put out the power they need to maintain the desired speed. As the second fuel (propane) is added, your need for diesel to supply the power to maintain speed is reduced and you reduce your throttle application. BAM! higher MPG of diesel. If you actually measure the amount of diesel AND propane consumed, you will actually see LOWER MPG. That's because propane has less energy per gallon than diesel.

Short version: If you want more power, turn up the pump. If you want better MPG, drive slower.

I have propane injection on my 240D and it adds a little to the power and efficiency. The propane that is injected flashes (burns) first because of pressure and helps vaporize the diesel. If I remember correctly (I did a bunch of research on this a few years back) an older diesel like ours in its prime will burn at best at 80% efficiency. Adding the propane increases that to around 90-95%. In my older 240D I was able to get 40+ actual MPG on the highway, up for 32 with the addition of propane. This would take about 10 pounds of liquid propane per tank of diesel and the added power would allow me to get up hill with out a problem where before I would loose a lot of speed. At that time the cost of propane was made up for by the better MPG, so I broke even and get some extra power for free. The 240D I have now is in much better shape, so better efficiency and so the propane does not do as much as it did in my older car. I’m going to be tuning the system I have later this spring, I have it hooked up to the kick down switch from an auto, so it only turns on when I have my foot in it hard. I only have just over 2lbs in the truck and having that on all the time would run out fast.
Here is a site about propane injection. Hope this helps.

http://www.mrsharkey.com/lpg.htm

Almost all (99%+) of the diesel is burned when there is enough air to burn it. The difference between older and newer diesel is thermal efficiency and combustion design techniques.

Wow! Great link Graminal95! That sums it up completely. Propane offers a slight increase in efficiency since it helps the diesel burn more completely. It also offers modest power gains if used sparingly. Turn it up too far and you will break something.

RT

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Yeah really, can you imagine how much smoke there'd be if 15% of the fuel wasn't being burned? Huuuge amount, also, fuel economy would stink, and the exhaust pollution levels would be immense. Diesels burn essentially all of the fuel put in the cylinders, unless you're putting in more than the design of the engine is capable of burning.

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So my memory fails me again. I went and looked up some info in my thermodynamics of internal combustion book and you guys are correct, it is a much better burn then I stated. It appears that the rate of combustion has an effect of the power output a few hp difference from 600 1/s to 800 1/s and I suspect that the propane helps to make a faster burn and thus an increase in power. Any other thoughts on this?

From what I have read propane wont auto cobust in a diesel engine. I think the power gains are made from the propane continuing to burn after the diesel is gone. And if thats the case I can see how it can improve fuel efficiency. I remember years ago reading about natural gas systems for diesel engines to improve fuel efficiency.

I set up a really low budget test system on my 1986 Ford F250 diesel pickup. That truck uses an IDI 6.9liter V8 , technologically, quite similar to our Mercedes. I simply set up 1 lb camping type of propane bottle between the seats, and ran a hose to the air intake of the engine. When I wanted additional power, I simply turned the knob on the bottle. There is nearly a zero chance of getting too much propane with this method--the pressures and flow volume are just too low. I noticed a slight increase in power--better acceleration on interstate highway ramps,especially usefulwhen towing my 25 5th wheel. I also noticed that I could maintain 5 mph or so greater speed on long grades of constant gradient--compared to not using the bottle.
My conclusion is there can be slight power gains,but w/o a pyrometer to measure exhaust temps,I would hesitate to use it for londger than maybe a minute at a time.
I know that my temporary test method was a potential hazard, especially in an accident. I don't need self-righteous do-gooders to preah at me. It was a test. It has been discontinued. If i were to install it for a longer trial, I would mount the propane securely out of the passenger compartment, and use proper valves and switches to ensure safe operation.

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how long did it take to go throught that 1lb bottle?

How long did it take to go thru that 1 lb bottle?

I can't recall exactly. I did use it sparingly, but I guess it ran about 1/2 to a full hour. But since I used it in 15 - 30 second bursts it lasted for maybe 500 miles of driving.
I would be very hesitent to use it on a long upgrade where I'm at WOT for a couple of miles as the exhaust temps might get to a critical point.

It might make sense for a 240D to give it a shot at WOT.

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If you do a little research I believe the Powershot 2000 is the most sophisticated unit. It is adjustable for delivery based on boost pressure, and then it will deliver progressively more propane as boost increases. The progressive delivery curve is also adjustable so the system can be completely tailored to your needs. The downside is cost, as usual. Although, having a fully adjustable instant hotrod for $1500 is not too bad if thats your thing..... RT

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$1500 would take a LONG time to make up for in MPG difference and the HP addition can be had by adjusting the injection pump for free.

I've looked into it quite a bit myself and I find some of Sharkey's conclusions to be a bit... optimistic. I like a lot of his engineering though. Like Forced Induction says, the gain is only because you are adding more fuel.

It works like this:
Propane is injected into the air stream, usually ahead of the turbo to increase the mixing.
The air and propane mix enter the combustion chamber on the intake stroke of the engine.
The intake valve closes and the piston begins the compression stroke. As the gases (atmospheric air and propane) are compressed they release heat according to Boyle's law.
At the top of the piston stroke +/- a few degrees the injection pump forces a fuel charge into the combustion chamber. The fuel is subjected to high heat from the compressed gases and begins to burn. Once the oxygen is reduced to a certain level by the burning diesel (depending on how much propane you are injecting), the hot propane gas reaches a proper air to fuel ratio and combusts, adding additional heat and pressure to the power stroke.

Diesel fuel will burn in a very lean environment. Propane won't. Unless you are fueling to the max, there is always going to be more oxygen than you need to fully combust the diesel. Propane also has a higher flash point than diesel and wouldn't combust on its own without the diesel to raise the temperature.

In the end, you might as well just add more diesel and end up with something far simpler. Contrary to what Sharkey states (again, much love) the efficiency of the combustion process is not made more efficient.

It's a little like saying your wood-burning stove is made more efficient by dousing it continuously with gasoline. Sure you burn less wood, but now you're burning gasoline too.

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