crazy idea- converting a gasoline engine to diesel
 

Has anyone ever heard of someone trying this?

I would want to start with a lawnmower engine:

Major differences/obstacles:

1. compression needs to be about 22:1 for diesel to ignite, gasoline engines are 9:1 so the head needs to be shaved a bunch or install a domed piston. Or a supercharger, Or another larger displacement engine (2X as large) feeding compressed air to a smaller engine that will run on diesel

2. with higher compression comes higher pressure on bearings and the block

3. a valve to meter diesel going to injector (to control engine speed)

4. injection pump (to pressurize the diesel or vegetable oil)- how about a power steering pump that was belt driven by the engine? These pumps will produce 1200 psi.- I have read that older diesels had injector pressures as low as 1700 psi, maybe a power washer pump- some of those will do 1700 psi.

5. injector (to spray the diesel in through the spark plug hole)- maybe a power washer nozzle.

6. something to time the injection- something like a rotary valve that would spin the same rate as the cam and could be indexed to inject the diesel at the peak of compression

Any encouragement, discouragement or ideas on how to do this on a budget?

The timing and metering issues seem like they will be the hardest to deal with.

you'll need a stronger block to handle that level of compression.

GM is a good example of why this is a bad idea, their engine blocks, heads, head bolts connecting rods, and nearly every part of their engine was not strong enough.
for a lown mower engine you are als going to need a heavy fly wheel, I would start out with at least 20 pounds to keep your lawn mower engine turning with the high compresion, put that on a stronger crank shaft, in a stronger block, basicy dubble what you have, either that or you could make a sleeve to reduce the engine boor by about half.
personaly, I would invest $1,200 in a hatz diesel to learn how they work, befor building your own but at that point you have a 8hp diesel that works perfectly.

Agreed. for the ability for it to run for more than 5 minutes before blowing up, you'll be better off just getting a small diesel.


yea...GM does a lot of things in cars that I'd NEVER do.

It's not a good idea. Parts 4-6 are the heart of a diesel, and it took Bosch many years to figure out how to do it without an air blast. It was many more years before they figured out small diesels, and direct injection in them is relatively recent. Gas engines are very simple compared to diesels.

Just buy one of the little diesels from China. Why spend so much time and money to end up where you can start? It's more interesting to do something new.

Lasting 5 minutes would be a success in my book if I spent less than $50 doing it and could reuse the parts on another project :D

I like the challenge of doing something new and different, learning from mistakes/failures and then trying to improve what went wrong (or deciding that its too much trouble to fool with).


Thanks for pointing out that it would need a very heavy flywheel (maybe a car engine flywheel bolted/welded to a pulley)

Any ideas for a cheap rotary type valve to time the injection pulse?

How about a way to meter the diesel?

I don't really need a small diesel engine- its just more of an enjoyment of tinkering and coming up with something interesting that might eventually be practical if the bugs could be worked out of it.

I've done several such cheap projects in the past (homemade trailer type backhoe and homemade band sawmill, installing points on a motorcycle with a bad CDI stator, lots of go carts when I was younger, being pulled across a pond by a truck and a long rope standing on homemade plywood waterskiis...) and so far I have gotten enough money or enjoyment out of them to justify the small investment in each project.

One of my failures was my attempt to install a woodburning stove in the yard (in a very small enclosure) and use ductwork (hot air and a cold air return) to pipe the hot air in through a garage window to heat the garage.

In short, I have lots of crazy ideas- some work, some don't (anyone recall my exhaust restrictor test? :eek: )

Well, before computer controls, they always used the pump to time the pulses. The idea is pretty simple: a piston pump is synced with the motor, so the peak pressure happens at the right spot. The pump has a rotating sleeve, controlled by the governor, which allows the diesel to spill out until it reaches high enough. All diesels need speed governors: they aren't stable like gas engines.

The injectors have a sort of poppet-valve in them, so that when the pressure is high enough it lifts it off its seat to do the injection. If it didn't do that, then diesel would leak in all the time, and the pulse would be too wimpy to really atomize the diesel.

The earliest ones were air-blast: they blew the diesel in with super high-pressure air, which atomized the diesel and more precisely timed the pulse. If you can't/don't want to get a real diesel injection pump and injector, that'd be the way to go. It needs to be a very fine mist to burn. Big drops just smoke a little, but don't burn.

Randy- thanks for all the info.

I believe my old diesel tractor uses the poppet style injectors, now I understand why they just can't be simple nozzles.

So how many psi would the air blast have to be? And how did they suspend the diesel in the air- in other words exactly how did the air force the diesel into the combustion chamber?

I read a book on the history of diesels once, which is where I'm getting it. Did you know that diesel did the first test with gasoline? It blew the pressure recorder across the room, nearly hitting him. He switched to heavier fuels at that point.

I think the air blast was around double the cylinder pressure, but I don't remember exactly. The fuel pump and injectors were nearly the same as now, but the poppet valve was on an engine cam. As it went up it shut off the fuel and intake to an air receiver, then opened the receiver to the injector, blowing in the fuel out of the injector. It was more complicated, but they got it working pretty quickly. At the very least you'd get an air-powered motor that can generate a lot of smoke. The more modern fuel-only design is much more touchy... I don't think there's much chance of getting one working without starting with one.

I've heard of some people doing it on 1.6 VW motors, didn't read much more on it. Back in the 80's we had a customer at our auto parts store that just got a Kubota tractor motor and installed it in a Bug. Phenomenal mileage.

Randy- thanks again for all the info, the air blast system seems pretty complex to fabricate.

I am now leaning more towards converting a lawnmower engine to a hot bulb engine, which could burn diesel, vegetable oil or even heavy oil. The biggest drawback there is that the efficiency of the hot bulb engines are lower than gas engines and they run very low rpms so power output is low.

nitromethane engines are basiclya hot bulb desine, only they have the heat source inside the tube insted of heating the whole tube.
our delco light plant generator is a multi fuel design that can suposedly run on kerosen and light diesel fuels, I haven't hauled it out of the shedto take a look at it in a while, bit if i remember right it heats the fuel, and has an adjustable ritchness carburator, a heavy fly wheel, and high compression, start it on gasoline, warm it up and switch fuels.

It is not what you are asking about but my old Briggs and Stratton maintenance manual has instructions for operating on fuel oil. Double up the head gaskets and set the points a little closer to retard the timing. You need to run on gas until the engine gets warmed up. John Deer tractors had dual fuel tanks to simplify this. When I was a kid I heard of a Buick that ran dual fuel. It had two tanks and two carbs. One fed diesel and the other fed gasoline. Again I know this is not what you are asking about but it is as close as you are going to get without getting in over your head.

I am sure it could be done but I can't imagine why you would want to do this. There would be little economic payback for a one off engine.

Wow- that's interesting. It surprises me that you would double the head gaskets (reducing compression) instead of installing an extra thin gasket to increase compression.

What age and hp of a Briggs is it? And how do they recommend you switch it over to fuel oil? A separate tank and use a selector valve to stop gas flow to the carb and begin feeding the carb fuel oil?

usedgeo

I found this discussion that describes what you mentioned:

https://groups.google.com/group/alt.e...709975bba86ed5

"Kerosene or diesel can be run on spark ignition engines of low compression
( they have a very low octane rating... ) if it's preheated first. Or if
its a high compression engine the fuel can't be in the chamber untill you
want it to lite..ie a direct injected engine of diesel type.... kerosene is
not used as a 'diesel' fuel because it is a poor lubricant and the injector
pump will not last
The reasion for the preheat is that the kero ( or diesel ) must get above
it's vapor point to be able to lite..
An interesting thing would to use a dual combustion chamber of the honda
CVCC type and have different fuejs in the combustion chambers.... gasoline
in the aux chamber and kero or diesel in the main chamber... no preheat
would be required, and probably less smoke... "

My car has the Honda CVCC, but I'm not sure I'm ready to start modifying it...

This doesn't sound very promising "They claim power loss
is 15 to 25% and fuel consumption is 15% less then running on gasoline. "

Wouldn't that mean the same fuel usage per hp?

I think they ment fuel economy droped by 15%, so the overal hp per gallon would drop by 30-35%, at least that is what I fould in useing biodiesel in my honda cb125, at 50% biodiesel the power droped, and the fuel cosumed jumped, it also would not rev past about 3,000rpm (low for a 125cc engine).

In the spirit of this thread (and not trying to hijack, Erik), if you're looking for something to tinker with:

I've often wondered what it would take to get an engine to run backwards. I never put much thought in it, but at one time I had many Honda engines in my garage, and casually thought one day about trying to get one to run in the opposite direction.

I think it could be done provided it had a lower output (as in ~10hp/L) compared to the SI equivalent and you always started it warm. Either warm it up via a carb for a multifuel engine or for just diesel use a block/grid heater to get it started. You will be hard pressed to reinvent an injection system IMO so your best bet would be to make a mount for an older IP and run the injectors in place of the spark plugs. Based on what I've read most problems with GM diesels originate from the crappy head bolts, which a stud kit is supposed to fix. The diesel blocks are also supposed to be a hot ticket item for building a HO gasser.

How a bout a 455 cid block? it can handle the compression. if diesel atomized at a higher pressure then you would have to get a smaller metoring nettle in your carburator with higher pump pressure and maybe a fuel shut off so it doesn't diesel (run when shut off). I don't see why it cant be done. I am interested in trying this 92 octane to a 25 diesel octane if it is possible. let me know. maybe if you rigg up a turbo or a supercharger. it could work.

The tractor that ran diesel or gas is called a Poppin John. It's by John Deer and ran dual fuel.

Also stated above it is possible to run a B&S on kero. Just has to be hot first. Problem is you can't shut it OFF!

Just stick your hand over the carb :D (I have to do that to prime my lawnmower all the time..)


Let us not get confusiated, there's two ways of running diesel... compression or spark ignition. With hot diesel and lower compression you can run it under spark ignition in a gasoline motor, or for compression ignition you need the compression higher. Retarding the cam enough so that the intake is open some time after TDC, reducing dynamic compression, might be a temporary measure to get a motor running on whatever the heck fuel you can find for it, veggie oil, kerosene, varsol, white gas, bunker fuel, jet fuel...

You might get compression ignition working by threading slugs into the plug holes, depending how much piston clearance you've got, M18x1.5 bolts might take up enough room in the chamber to let diesel go bang. Typically this would be in a head that was on the high compression side in the first place where losing about 3cc would make a difference. For instance a 1.6 motor with 11:1 compression might go up to 12:1 and just about make diesel bang with a slug in the plug hole.

The thing I'd like to try however, is compression ignition on gasoline with diesel to fire it... yeah, that's sounds wierd don't it. Well gas has low cetane rating, diesel high, now if you get some really good diesel, high cetane, then when a charge of gas is in the cylinder under compression and you just squirt an itsy bitsy bit of diesel in there... it will fire off... so instead of plugs you could have small diesel injectors, very small, and you barely need much diesel at all. I think this could fire far leaner mixtures (even accounting for the diesel use) than plugs could.

I P'd-O my dad once when I was a kid. I took it upon myself, without his consent, to clean and gap all three sparkplugs in his, back then, nearly new 1965 SAAB. All was fine until I mixed the plug wires.
From being timed slightly advanced they were now significantly advanced, and although still in phase, were transposed by one cylinder. He cranked and cranked it finally backfired and ran, but the little two stroke was now running backward. Due to the freewheel mechanism there was no forward motion as the ratchet on the input shaft was spinning wrong way 'round. He locked out the freewheel for direct gearing and then found he had one gear to move forward (reverse) and four to move backward.
It was painful to sit in the next few hours after he figured out what had happened and found where I was hiding.

'58 Dkw
 

I cut my car teeth on a DKW (Deeke). It was manufactured by auto union in Germany (predecessor of Audi), and that 3 cylinder 2 stroke was a piece of work! Saab used that engine in some of their earlier cars. I would love to try converting that 2 stroke to diesel operation. I am a new member and have sure enjoyed this thread, every single contribution. I am the new proud owner of a 1990 carburetted Subaru Loyale that I am going to experiment with various fuels in. (Bad Grammer there, I know.) It cost me $51. It was originally offered to me for free but that offer was made at amnesia brewpub in NE Portland and then the scrap metal man offered $50 so I had to beat his price. If the experiment works, I'm going to try it in my '74 chev bread truck. Thanks guys (girls?) for the education and the entertainment.

Just an FYI, a lot of diesel engines sold only have 17:1 compression, not 22:1. Depends on the maker tho.

A TOTAL waste of time.
There are so many design aspects that clash that even a redesign of a gasser engine is a mistake, just ask GM!

You will never get the compression ratio you need without stretching the stroke beyond the limitations of the block because if you just dome the piston and fly-cut the heads enough to shrink the combustion chamber the deck will be too thin for even the stock compression ratio, and the valves will hit the piston when they start to open.

Well, try something that has not been done before or a new technology, and save time by learning from the mistakes of others, not duplicating them.

There is a lot of work being done to produce "Browns gas" (Hydrogen and Oxygen split from water) and there is much more to be tested.

remember the old rabbits,,,, they tried it ,,, head gasket night mare

I recall back in the '70's a front-end loader I used to operate that a shop had converted to diesel. It used glow plugs drilled into the cylinders and was a ***** to start. It didn't have a ton of power either, but they used it every day, working hard. Only other thing I remember about it was it was a straight six.

Get a helmet and a body armor suit before you try to start it.

Erik, where'd you go? I was thinking about the same exact thing. Starting small on a lawnmower engine is a good idea, but my main thought was to run indirect injection diesel (like an old Merc carb) for the main charg on the CVCC and then regular gasoline for the pre combustion chamber. I figure this should easily light off and work ok at the stockish 9.5:1 I'm shaved up to.

Of course I haven't really pulled the intake manifold but from looking at the head I can't really tell how the precombustion chamber gets it's charge and I'm not sure you can easily seperate this to a different runner for a gasoline carb. I would think if I could (or had any kind of welding fab skills) then a single side draft motorcycle carb should be enough for that chamber. The diesel with an old carb shouldn't be too hard, I'd really want a way to lean that out even more though. I mean I bet you could get to the point where the diesel would ignite at 50:1 and also at 25:1 or something so I could basically choose if I wanted half the diesel and half the power for cruise and idle.

Mostly I just want to start making biodiesel and any cheap old, crappy diesel car I look for is easily over $1000 which is too much.

The other thing I wanted to do, I have an old 4 cyl 550cc Suzuki engine doing nothing and would love to make it a 2 stroke turbo diesel. I have an old Turbo off a 2.2L Chrysler something and while that might be enough with some planning to get to good compression ignition, I'd like to go further and try to make it 2 stroke. That is, some kind of valve on the side of the cylinders for intake and same sealed oil as a 4 stroke and then EVERY cycle the intake opens at BDC or just before and closes a little ways up, maybe 45-60 ABDC and then compression, injection and ignition and about 45-60 BBDC we open exhaust. Close it 5-10 deg after intake opens for some scavenging (easy with a turbo pressurize intake). That way you get twice the power out of a smaller engine. Of course the main purpose in this was define some way for the engine to 'free wheel' or skip cycles if I chose. I like to be able to run 1 ignition even every 2 revs or every 3 revs or 1 rev (which is 2 stroke) on demand if I can. My main goal in either design is so I can more easily chose the amount of gas I'm giving and the amount of power I'm getting out so I can match it up to load for fuel savings. If possible I should be able to save a lot with either design.

The bonus with the motorcycle engine is that my CRX is an automatic and if I could somehow get the 2 stroke turbo diesel going and wedge it into the CRX I'd have a manual. Of course coasting would still be a pain because it'd be a sequential tranny :p. Of course either requires tons of fabrication skills which I don't have. I do have a welder I bought but can't find scrap metal and don't know how to start learning and don't have any time.

Keep me updated!

I haven't done anything with this idea yet- I have been leaning more toward a hot bulb low rpm lawnmower engine with a large flywheel that burns used motor oil. Maybe next summer when I have more time. I am rebuilding a 10:1 compression 1.3 liter engine right now to swap for the 9.2:1 compression 1.5 that is in my civic.

The CVCC precombustion chamber gets its charge through small valves on the exhaust side of the head (you can see them if you take the valve cover off). They have separate intake runners that lead to the tiny offset barrel on the carb.

Do you have your CRX running yet? I have been leaning out the mix on my 87 CVCC civic with good results. I'm planning to switch to an HF carb and see if that helps even more.

Good luck with the 2 stroke diesel idea- you'll have to take lots pics of steps along the way.

If you have no engine or tans in the CRX- how about hooking the suzuki engine to one of the half shafts of your CRX? It would be interesting to drive around for one tank to see what type of mpg you would get with the weight and displacement reduction. I bet it would pull toward the wheel that wasn't getting the power though.

Hahaha I like that idea. Yeah I totally don't have any idea about how to hook it up to a tranny and what not.

No, first step is getting the CRX back together. The engine is just about all set, but I need to figure out the wiring and vacuum mess :(. Yes, I too thought that leaning the main chamber and keeping precombustion as stoic or a bit rich should work great, but there has to be some limit where it's so lean it'll self combust due to compression, right? I also shaved my heads and grooved them while they were off, we'll see if that does anything. And no, engine and tranny were in the car it just came with the head off and everything else under the hood in the trunk. He was planning an Acura swap. Which honestly I would have done but couldn't find any engine/tranny combos for less than $500. But DOHC and 5 speed would have been sweet. I really like the CVCC design though, I want to tweak it and see where it takes me.