Spark Ignition Diesel ?? - RC Groups
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Jul 19, 2012, 08:42 PM
Registered User

Spark Ignition Diesel ??

Several years ago DARPA asked for UAV engines to run on diesel (heavy fuel) or jet fuel.
The solution that I saw the most was modifying an engines ignition system to be
compatible with either fuel.

My question is:

1) Why isn't gas pump Diesel (heavy fuel) being used in gas engines?

2) Theoretically speaking, what is required to convert a weed whacker
to run on diesel fuel. And does (gas pump) diesel fuel contain enough oil to lubricate
a two stroke motor?

Would increased compression ratio be necessary if it was spark ignited?.

Diesel fuel has a greater density than gasoline, but nearly the same stoichiometric
fuel to air ratio as gasoline. For modifying a carb, maybe some orifice area
changes, and possibly adding a air-bleed circuit to the hi-speed fuel circuit. Walbro's
already use an air-bleed system for the low speed circuit, so more orifice area
changes may be necessary.

What are your thoughts, thanks

Bill M.
Last edited by Capt. Quirk; Jul 19, 2012 at 10:51 PM.
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Jul 19, 2012, 09:05 PM
Methanol, The Cool Fuel !
Gary Cee's Avatar
Diesel has a lower octane and runs better on low compression with spark igntion . Vaporization and cold start are other issues . My first car was a Ford Model A . The original owner drove the car during WW2 mostly on fuel oil . He rigged a 1 gallon can to supply gasoline for starting . Once started and warm he would turn on the main fuel tank (Gravity fed, cowl mounted tank) ..and turn off the gasoline .

Multi fuel stationary engines were quite popular in the early days and ran on many fuel types with spark ignition . Kerosene , coal oil , naphta , wood alcohol etc were popular fuels .
Jul 19, 2012, 09:36 PM
Registered User
I TOBOR's Avatar
This tractor had a three valve head to start on gasoline and when warmed up the third valve closed increasing compression from about 6.5 to 1 to 16 to 1 and covered the sparkplugs. 16 to 1 was marginal as the engine would not direct start even on a 100 degree day unless you rolled it down a steep hill fairly fast. Pump Diesel would wet spark plugs instantly.

Pump Diesel works in Diesels because it is injected into red hot air that is glowing at 1,000+ degrees. When you compress 60 degree air to 363 PSI it generates 1,000 degrees of heat and glows a dull red. Most Diesels compress the air 650PSI or better.

Our model Diesels work at say 12.5 or 13 to 1 because of the ether in the fuel. The Saito .80 pictured is happily turning a Bolly 13.5x8 at 8,792 rpm on Davis Diesel Developement ABC mix. Its compression ratio 15.6 to 1.
Last edited by I TOBOR; Jul 19, 2012 at 09:46 PM.
Jul 19, 2012, 09:38 PM
Hope to get out of life alive
kenh3497's Avatar
WAY back in the day many farm tractors would be started on gasoline and the switched over to "distillate" after they were warm. I assume the distillate was nothing more than a form of diesel fuel or kerosene.

Often times water was added to the mix to give extra power and cooling. Yes Martha, you can run an engine on kero and water. I've done it!

Jul 19, 2012, 09:50 PM
Registered User
I TOBOR's Avatar
Ken, we had a McCormack Deering F 12 on our farm that ran on distillate, the intake and exhaust manifold were cast together creating a huge hot area above the carbutetor, even the paint on the intake manifold was scorched.

Here is an F-20 where the intake is scorched in the center.
Last edited by I TOBOR; Jul 19, 2012 at 09:58 PM.
Jul 19, 2012, 10:28 PM
Registered User
earlwb's Avatar
Well the military have been using multi-fuel vehicles for quite a few years now. I remember them having them way back in the early 1970's/ The standard military cargo trucks all had the engines in them. They could burn gasoline, diesel, JP-5, some distillates, and kerosene probably too.

There was someone trying to sell a Quadra or Zenoa engine on ebay that was converted to run heavy fuel. But no one bid on it as he wanted too much for it. I remember someone else putting up a fuel injected heavy fuel two cylinder engine and he wanted way too much for it as well. I don't think they got anyone to buy the things. I might have gone for one, if the price was low. But I didn't want to pay a high price for a fancy doorstop conversation piece.
I have plenty of that kind of stuff already.

JBA engines a couple of years ago made a 15cc heavy fuel spark ignition engine, but the military bought up the entire production run from them. So we didn't get a chance to get any ourselves.

The heavy fuel (like pump diesel) might work with a glow engine carb, as the fuel is heavier or more thick than gasoline is. So I don't think that one needs a complicated gasoline pumper carb for it. But you may have to heat up the engine or preheat the fuel to get it to burn better in the engine. The trick is whether the air/fuel ratio can be worked out enough to get a engine to start so it can warm up and run better off of the fuel or not. I remember some guys using regular model diesel fuel to start the engine and then switch over to straight diesel afterwards. But the model diesel engines were not all that happy with the fuel though. Thus your thoughts on using a spark ignition system would tend to look pretty good and ought to work.
Jul 20, 2012, 06:19 AM
Methanol, The Cool Fuel !
Gary Cee's Avatar
It may get confusing for some if aren't clear that we are talking about diesel or kerosene with SPARK ignition . Fuel vaporization with spirits (kerosene/diesel) fuel is often promoted by heating the intake area .

The dual fuel , diesel / compression igntion is another animal .
Diesel fuel with spark ignition will need a fairly low compression ratio . Diesel/compression ignition are the high compression engines..a different animal .
Jul 20, 2012, 07:19 AM
Dieselized User
gkamysz's Avatar
The only people that want to run small engines on JP-8 (NATO F-34, kerosene) is the military. That's why it's not common. Yet, if you wanted an engine like this you could contact any of the top end model engine suppliers and get one.

The spark ignition system is not the problem. The trouble is cold starting a fuel with very low vapor pressure and getting enough power/efficiency.

Jul 20, 2012, 08:02 AM
Methanol, The Cool Fuel !
Gary Cee's Avatar
Originally Posted by gkamysz
The spark ignition system is not the problem. The trouble is cold starting a fuel with very low vapor pressure and getting enough power/efficiency.

Yessir ,
The cold starting issue is precisely why the fellow I bought my Model A from started on gasoline , them switched over to kerosene/fuel oil . The Model A had a couple of features that helped in the dual fuel operation . The fuel shut off was inside the car on the passenger side , easily reached while driving . The high speed mixture was combined with the choke knob, pull to choke and turn the knob for mixture . The spark timing was also adjustable at the steering wheel .

Starting of spirits fueled spark ignition engines on gasoline is pretty common for the dual fuel runners .
Jul 20, 2012, 11:38 AM
Registered User
Had a fellow come with a chain saw to do some tree trimming. It was really difficult to start, and when finally running, smoked a lot. It was way down on power, and he gave up. It turned out that he had fueled it with pump diesel rather than gasoline. He came back later with gasoline and finished the job.
Jul 20, 2012, 11:54 AM
Dieselized User
gkamysz's Avatar
It should be noted that pump diesel (DF2) is quite a bit "heavier" than the JP-8, which is basically kerosene, the military uses.

I run my four stroke diesel conversions on kerosene with no problem. Pump diesel doesn't work. That is to say that I have not attempted to optimize and engine for pump diesel as the stuff is messy and smelly. Kerosene will evaporate in a fairly reasonable time.

Jul 20, 2012, 12:40 PM
Registered User
earlwb's Avatar
That sorta reminded me of the TV show "Then Came Bronson" when he stopped at a small store/gas station and the lady filled the bike up with Weed killer. He fired the bike up and was getting ready to take off when the lady came out all freaked out and told him about it. Yes he had a great look on his face about it at the time too.
Jul 20, 2012, 02:18 PM
Registered User
Would preheating the diesel fuel before the carb assist in starting the engine?
Jul 20, 2012, 03:26 PM
Registered User
earlwb's Avatar
I had those same thoughts about preheating the fuel up good. They do that with the big monster engines that burn that bunker oil fuel in the ocean going ships. They also do it in the big steam engines on the train locomotives too.
Jul 20, 2012, 03:36 PM
Dieselized User
gkamysz's Avatar
Bunker C oil needs to be heated to pump and inject it. At room temperature it's as thick as thick honey.


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