Diesel

So I've read in a number of forums that diesel is not suited for use in small engines because the level of compression needed for proper combustion cannot be achieved.
Is this true, and if so, to what extent?
Would, say, a 1/10 model of a v 12 diesel not achieve proper compression, but a 1/4 scale might? Where is the line?

Is there any way to mitigate this? The idea of a small diesel fascinates me, and I'm sure quite a few other members have looked into this as well.

~Shinhoto

From what I understand, the main problem is the fuel injection system. Getting such small injectors to properly atomise the fuel to allow combustion seems to defeat most attempts. I think there's a couple of 'true' model diesels that have been successfully built but I don't know what sort of scale they are (I'm thinking I saw a single cylinder around 1" bore on youtube a while back but not 100% on bore size). I did see a poster from a couple of years ago building a scale Cummins inline 6 and he was doing an amazing job of it, but I never saw it completed so I imagine he ran into the injection issue and either gave up or is still struggling with it.

Okay thanks. Do you have a link to any of what you've mentioned?
I might like to try to build a 1/6 inline 6 diesel with a stroke dia. Of 0.85 inches.

Following on from Cogsy's reply, I believe model diesel engines use kerosene for fuel and not true diesel fuel, because of the atomised particle size.
No doubt someone will tell me I'm wrong and true diesel fueled diesel models have been built. (Yes, I have seen one about 8 years ago - a 4 cylinder free-lance model over on the west coast of the USA but man, did it smoke!)

Dave
The Emerald Isle

Here we have the 4cyl. Cummins diesel

CS

Wow that's an amazing engine. Is there a way I could get in touch with it's creator?

Shinhoto said:

Wow that's an amazing engine. Is there a way I could get in touch with it's creator?

Click to expand...

He have more engines/videos on You Tube.
https://www.youtube.com/channel/UCVwcGVPSXDIp-6QHPb-VcnA
CS

Look at this clip . He is a amazing engine builder.

Bengt

wow man this guys got some skills

Hi shinhoto
Building a model diesel is quite challenging at best. I have spent the last three years building one with various degrees of success. To date, I have made twelve injectors and ten pumps and non that I would say we're successful. The problem is the high pressures ( 2 to 3 thousand pounds) involved with solid injection. The problem is that you can scale the model but you can't scale the physics.

The injector built by Finds Hanson is what I would call a spray nozzle which works at a much lower pressure. But you have to give it to him, it works and I would suggest that the fuel is not diesel. He is quite a craftsman and is due appropriate praise.

I would suggest you start with a single cylinder engine say 1:6 or 7 scale and there are some good examples around. A spray nozzle is probably easier to make. If your a tool maker or similar with 40 years of experience you may be able to get solid injection to work. All of mine were based on the CAV/Lucus type and I have both surface and cylindrical grinding available but could not do better than 2000 psi. The problem with diesel, is that it needs to be atomised which means high pressure.
There are several good books 1900 era which are free on the net if you know where to look and give you a good insight as to what will work

My current diesel model is a 1904 air blast injection engine which to my knowledge no one has achieved in a model. I have a thread which I will updat next week some time.

If you are interested in the URL of the books send me a private email. I could also provide you with plenty of other info if required.

Bruce W-S

deverett said:

Following on from Cogsy's reply, I believe model diesel engines use kerosene for fuel and not true diesel fuel, because of the atomised particle size.
No doubt someone will tell me I'm wrong and true diesel fueled diesel models have been built. (Yes, I have seen one about 8 years ago - a 4 cylinder free-lance model over on the west coast of the USA but man, did it smoke!)

Dave
The Emerald Isle

Click to expand...

Kerosene is #1 diesel fuel.

I worked in the injection equipment area designing and testing injection equipment. It would be very hard to scale down a direct injection pump (1500 bar) to overcome compression. The main problem is the tolerances required to produce these pressures (in many cases sub micron). It would be much easier to create and indirect injection system (500 bar) which injects close to bottom dead center and compresses the air and fuel together during the compression stroke.

Beyond the fueling problem is that leakage around the piston and valve seats has to be minimized to produce the necessary pressure for ignition. The requirements would me minimized if model airplane fuel was used (lower pressure to ignite.

In the late 60's the US military had multi fuel engines which could run on diesel kerosene aviation gas or even vodka. The engines did run better on diesel or kerosene.

@weir-smith. Hi I realy dont know if Find Hansens injector is a spray nozzle.
Look at the clip from 22:00 and tell me what that is.


Bengt

The injector is of a pintle valve design. I would expect the opening pressure is about 50 bar (725 psi). The opening pressure is set by the spring load which is holding the valve closed. The nozzle chatters due to the rapid reduction in pressure when the valve opens which causes the valve to close and the pressure to rise and the cycle repeats. As was stated in the video the cone angle is adjusted by the angle of the pintle valve.

Thanks for your answer.
Bengt

Machinist mate of mine from Australia has a Lister diesel engine he built on Youtube....look for George Punter Lister Diesel

I remember seeing a series in a magazine about an engine like George has made , cant remember which mag but it would have been either model engineer or Australian model engineer magazine .

Model Engineer mag but sorry no more detail of date etc

I recall one of these was a converted milking machine but used to drive a ski tow.
Don't ask


Norm

It was within the las three years I'm sure . Or is time now slipping by me at a rate i cannot comprehend !