Centaur model gas engine

Not your normal full sized engine but a model I made a couple of years ago.
It's been run on petrol and is designed to also run on gas, probably the old town gas. I would like to run it on gas, specifically a propane/butane mix.
My first attempt at this today was not a total failure - but almost!
I believe I need to regulate the gas supply, today's attempt was with the gas valve open to allow a 'trickle' of gas through. Managed to get it to run for a short while but then I think I flooded it with too much gas?
Couple of questions, would it be better running on straight propane? and what sort of gas pressure should I be aiming at?

Alan

Not played with models on gas but when the big gas engine was installed at the Pitstone museum it wouldnt run on straight gas and needed a gas bag so the engine sucked what it needed and not pressure fed.

Maryalice

Hi Alan,
I have just got my Centaur running on gas. It refused to run on petrol, only firing occasionally. I hitched it up to my straight propane bbq bottle and it ran better, but not consistently. In order to conduct experiments to try and understand how various fuel supplies affect running, I then ditched the regulator on the bottle and connected it directly to the engine, with positive results.
The bottle needs only to be cracked open a tad and likewise, the carburettor needle valve is only just open, and the air valve three quarters open, but it runs and consistently. I can vary speed between an estimated 400 to 800 rpm and likewise adjust speed using the advance/retard lever.
I recognise that unregulated gas is NOT the ultimate answer. It has informed me on fuel supply characteristics and I now need to work out which regulation is best.
Kevin.

Kevin Parsons wrote:Hi Alan,
I have just got my Centaur running on gas. It refused to run on petrol, only firing occasionally. I hitched it up to my straight propane bbq bottle and it ran better, but not consistently. I then ditched the regulator on the bottle and connected it directly to the engine, with positive results.
The bottle needs only to be cracked open a tad and likewise, the carburettor needle valve is only just open, and the air valve three quarters open, but it runs and consistently. I can vary speed between an estimated 400 to 800 rpm and likewise adjust speed using the advance/retard lever.
Kevin.

I would strongly advise against doing that as depending on ambient temperature you can get 300+ psi out of the cylinder and I suspect your pipes/hoses could fail.

Point taken about the unregulated tank pressure!
Kevin, didn't know you was on here!
Just had a hookup to my gas cylinder with 30% propane and 70% butane (cylinder pressure is 40psi) and using a gas valve on the cylinder I ran engine up to speed and gradually opened the valve to allow gas to flow - it fired readily and sounded great.
Seemed to warm up a lot quicker running on gas and it wasn't happy after a while as it appeared to be missing the lubricating benefit of petrol with a dash of oil in.
I think to run permanently on gas it would need an injection of oil to be carried into the cylinder, so will stick with good old unleaded!
Kevin - have you run yours for long periods?
Video of it running (original quite good but has lost something on the upload!)

Alan
https://youtu.be/hg6pcgTcr_Q

I have just converted a lister D to run on propaine. This is via a regulator and a demand valve. This only allows gas to pass when ther is a vacum. ie the cylinder is on induction stroke. I have never seen a gas engine runing without a regulator! Dont think thats a good idea.

A hot topic!
As can be seen the throttle valve closes off two ports in it's seat, one for petrol the other is the gas entry.
While I will agree the supply should come from a regulated supply and if my trials had proved more successful this is what I was planning to do.
However!

Alan

Thats interesting. As long as the gas presher dose not overcome the spring.

dunitrong wrote:I have just converted a lister D to run on propaine. This is via a regulator and a demand valve. This only allows gas to pass when ther is a vacum. ie the cylinder is on induction stroke. I have never seen a gas engine runing without a regulator! Dont think thats a good idea.

Dunitrong,

Thats interesting, I have a D type and a demand valve which I have got to make a new diaphragm for, I found a company who supplied me with the material. I also have a D type carburetor which has a gas connection, could you show a picture of your carburetor please.

Maryalice

maryalice wrote:

dunitrong wrote:I have just converted a lister D to run on propaine. This is via a regulator and a demand valve. This only allows gas to pass when ther is a vacum. ie the cylinder is on induction stroke. I have never seen a gas engine runing without a regulator! Dont think thats a good idea.

Dunitrong,

Thats interesting, I have a D type and a demand valve which I have got to make a new diaphragm for, I found a company who supplied me with the material. I also have a D type carburetor which has a gas connection, could you show a picture of your carburetor please.

Maryalice

It was you that started me down the road to convert a D. You where on another forum. I looked for ages for a demand valve that was cheap and two years ago my son bought me one. We now have a BSA 420 and a villiers 20 that run on lpg. Sorry for going off post.

Alan,
You said:
Seemed to warm up a lot quicker running on gas and it wasn't happy after a while as it appeared to be missing the lubricating benefit of petrol with a dash of oil in.
I think to run permanently on gas it would need an injection of oil to be carried into the cylinder, so will stick with good old unleaded!
Kevin - have you run yours for long periods?

I found it warmed up quickly, and was run until the water tank ( the shell case) became hot for 3/4 of its height. Oiling did not seem an issue, I have the drip into the cylinder, and also a splash thrown up by the big end. I need to run it for longer to check if this is sufficient.

This is my convertion of a D carb. I bought a cheap D for £25 in bits, Its now runing but witha battery and coil.

Thanks for that, mine is still a petrol carb with a gas connection into the airvalve chamber.

Maryalice

The key here is the pressure of the gas. I think I read somewhere that these type of engines running on bottled propane/butane require a gas pressure in the region of 10 inches of water (an old measure for gas pressure). This is about 0.36 PSI (pounds per square inch) (or 25 mbar). So you need a low pressure regulator (and/or a demand valve) which will deliver this. You may also need a high pressure to low pressure regulator, before the low pressure regulator as some are only low pressure input to start with, to obtain the sensitivity required.

This is only an opinion, I am not an expert on gas regulation, but have fiddled with it on small power engines over the years. It can be tricky and fiddly to get right.

There is a air regulater that we used on air lines.This was to time a air circit.It only allowed air in one direction.And this could me finley controled. I saw at a show where some one used this just before the cab to fine tune the gas. This was on a big engine.

Interesting, I might try and put a suitable pressure gauge (water tube?) on the gas line to determine the pressure that lifts the air valve off its seat. I see regulators are readily available for pressures of 25-35mb
As for lubrication perhaps I need to experiment with the drip rate although I feel the moist vapours involved with petrol will definitely assist upper cylinder lubrication.

Alan

When I had a Tom Senior I converted an old Calor regulator to a demand valve. I just need to dismantle it, remove the spring, drill a hole and fit a long threaded rod so the spring was now external... if that makes sense...



Worked well enough

[quote="dunitrong"]This is my convertion of a D carb. I bought a cheap D for £25 in bits, Its now runing but witha battery and coil.

[url=https://servimg.com/view/20096287/4][img]https://i.servimg.com/u/f97/20/09/62/87/carb10.jpg[/img][/url][/quote]

A proper D gas carb doesn't have the hole on the side above the main jet.

Appletop wrote:

dunitrong wrote:This is my convertion of a D carb. I bought a cheap D for £25 in bits, Its now runing but witha battery and coil.

A proper D gas carb doesn't have the hole on the side above the main jet.

Thats interesting. I have never seen one so can you show us one? I must be honest i did wonder about the hole. Next  time i run it i will try blocking the hole and see what happens.

Just been out and run the D for a short time. Put finger over hole (risking burns from exaust) it made no diffrance. Can some one explaine to me what the hole is for. I thought it was for the engine if it backfired.

I've just read the Lister D bible to remind myself and a it says that your mod is close to that designed by lister so the engine could run on petrol or gas, a T tap was fitted in the fuel line tp drain the petrol from the pipe before running on gas.

Maryalice

I've heard of a demand valve but never understood what exactly it is!
Looking at the cross section of my model carburettor I can see how the gas supply is in effect 'off' until the valve is lifted by engine vacuum which will then allow gas to enter with incoming air charge.
I can also understand the need for a regulator although the original engine/carb build details didn't specify what pressure should end up at the valve.

Alan

After Maryalice saying he had a gas carb i started serching net for D gas info. Convertion sets where sold i think in Norway. I also found that the gas enters some as petrol and the mixture control is blocked off. So that it what i did. You can control the mixture a little with the air valve. Alanengine I must say your engine looks brilliant ! If only i could do the same.

Is there nobody on hear with a D runing on gas? I would love to see a genuine D gas carb Arthur

Genuine Lister D gas engine are like hens teeth, no pictures in the Bible, Calor made a conversion kit, I seen them on Wolesley's but not Lister D's, you need a demand valve and a regulator to run gas engines safely, I will dig my demand valve out at the weekend and take a picture.

Maryalice