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Stubby79 · 02-09-2017, 12:18 PM

There are issues trying to run a diesel engine on propane (I've looked in to it!). First of all, you need to rig up a distributor on something that has never been designed to have one. Possible, but I doubt you'll find off-the-shelf parts to fit.

Secondly, from what I read, propane is best run on low to middling teens CR. I assume this means to go past that, it is going to compression-ignite(which probably won't bother it), or just plain cause knocking(which will).

From what else I've clued in to, it's not just the more modern direct-injection and or common-rail that time the injection at just the right moment. The older, mechanical indirect injection engines do too. They inject it at or a hair before or (as I believe it actually is) after the piston hits TDC, to control when ignition occurs. If it happens too soon, the piston coming up is going to hit all that combustion pressure and bad things are going to happen to the inside of your engine. If it happens too late, well, it might not ignite, or you've just wasted the most efficient time for combustion and lost power.

This explains why the fuel is sprayed straight in to the combustion chamber...if it has to be precisely timed, you can't spray it in advance of said moment. Otherwise diesels would just use a single injector like throttle body injection and be done with it. Probably at a much lower pressure, since they don't have to overcome combustion chamber pressures. All this explains why there's an injector for each cylinder, and why they run the injector pump/nozzles at 1400+ psi.

Anyway, if you introduce another form of fuel before the injection moment, chances are that it's going to ignite before you want it to. And presumably why "they" don't really recommend it. And those who do highly recommend running an exhaust-gas-temperature gauge if you do, as it will help give you warning before you do damage to your engine.

Kubota specifically state in their manual that the introduction of any form of gaseous fuel in to the intake will void your warranty. And, supposedly, it's very easy for a technician to identify that this was the cause of engine failure. Meaning no using ether to help start 'em in the cold. Or any other uses of various fuels. Which has me thinking that if I do run propane on mine, I'm not going to do it to run it as a bi-fuel engine, but only just enough to give me a more thorough and clean burn of the diesel. I'm thinking 5 or 10%, no more. Enough to reduce unburnt fuel and maximize efficiency.

I love the idea of getting a third or more of my fuel/energy from propane, but I'm going to be very careful if I start messing around with it. First I'm going to see how well small spark-ignition engines take to running on straight propane, and take it from there.

Well, those are my thoughts on the topic, after my research. Hope it helps someone else.

02-09-2017, 12:18 PM	#61 (permalink)
Stubby79 Master EcoModder Join Date: Sep 2012 Location: Victoria, BC Posts: 1,747 Firefly EV - '98 Pontiac Firefly EV 90 day: 107.65 mpg (US) Little Boy Blue - '05 Toyota Echo 90 day: 33.35 mpg (US) BlueZ - '19 Nissan 370Z Sport 90 day: 17.19 mpg (US) Thanks: 75 Thanked 577 Times in 426 Posts	There are issues trying to run a diesel engine on propane (I've looked in to it!). First of all, you need to rig up a distributor on something that has never been designed to have one. Possible, but I doubt you'll find off-the-shelf parts to fit. Secondly, from what I read, propane is best run on low to middling teens CR. I assume this means to go past that, it is going to compression-ignite(which probably won't bother it), or just plain cause knocking(which will). From what else I've clued in to, it's not just the more modern direct-injection and or common-rail that time the injection at just the right moment. The older, mechanical indirect injection engines do too. They inject it at or a hair before or (as I believe it actually is) after the piston hits TDC, to control when ignition occurs. If it happens too soon, the piston coming up is going to hit all that combustion pressure and bad things are going to happen to the inside of your engine. If it happens too late, well, it might not ignite, or you've just wasted the most efficient time for combustion and lost power. This explains why the fuel is sprayed straight in to the combustion chamber...if it has to be precisely timed, you can't spray it in advance of said moment. Otherwise diesels would just use a single injector like throttle body injection and be done with it. Probably at a much lower pressure, since they don't have to overcome combustion chamber pressures. All this explains why there's an injector for each cylinder, and why they run the injector pump/nozzles at 1400+ psi. Anyway, if you introduce another form of fuel before the injection moment, chances are that it's going to ignite before you want it to. And presumably why "they" don't really recommend it. And those who do highly recommend running an exhaust-gas-temperature gauge if you do, as it will help give you warning before you do damage to your engine. Kubota specifically state in their manual that the introduction of any form of gaseous fuel in to the intake will void your warranty. And, supposedly, it's very easy for a technician to identify that this was the cause of engine failure. Meaning no using ether to help start 'em in the cold. Or any other uses of various fuels. Which has me thinking that if I do run propane on mine, I'm not going to do it to run it as a bi-fuel engine, but only just enough to give me a more thorough and clean burn of the diesel. I'm thinking 5 or 10%, no more. Enough to reduce unburnt fuel and maximize efficiency. I love the idea of getting a third or more of my fuel/energy from propane, but I'm going to be very careful if I start messing around with it. First I'm going to see how well small spark-ignition engines take to running on straight propane, and take it from there. Well, those are my thoughts on the topic, after my research. Hope it helps someone else.