Compression ignition

I am very interested in diesel engines. I have read multiple articles on true diesels needing atomization of the fuel and very high pressures to ignite. Then I have read articles on compression ignition with fuels like ether that combust at lower pressures but the fuel is hard to come by because of legalities and lack of interest etc. I want to build a compression ignition engines. Stationary horizontal type engines. I am planing on doing a few steam engines first, possibly a few hit and miss types. I eventually want to build a replica of an engine that my uncle had on his farm, a National Gas and Oil engine. I am just wondering what other easily come by fuels are there that can be used instead which don't need to be atomized and don't require such high pressures.

Any thoughts and ideas?

Thank you

I have considered building a true diesel with injector, but after reading about the trials and tribulations of others attempting it, I have changed my mind.

I would like to build a two-stroke diesel that perhaps does not require an injector, or one that uses a fuel system that is not very complex.

Perhaps not this large, but similar to this engine.
Maybe a hot-bulb type.

Rather iconic sound to it.

That boat engine sounds like an old john deere!

I appreciate the GM 71 series of two cycle diesels. Perhaps like you, I have followed them on youtube and followed the difficulties encountered when trying to build small scale models of true functioning diesels on this site and think about ways to make the injection capable of true diesel combustion. Fun to think about!

I worked at Cummins Diesel in Columbus, IN before production / assembly was moved to their new non-union facility in NY as a tool maker and greatly admired the efforts taken to hold tight, consistent performance levels in injection system function. Back in the early 80's their biggest issue while running new engines in test cells were with injector pumps and injectors as each new engine went into a test cell and went thru a complete thermal cycle on a dyno. That got reduced to only running about 5 minutes in an attempt to reduce costs.

Kegan said:

fuels are there that can be used instead which don't need to be atomized and don't require such high pressures.

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Liquids don't burn, vapours do.

So you are going to either need the engine to have enough heat mass to convert an incoming fuel to vapour OR stick with an atomizer that breaks the fuel into small enough droplets that they have sufficiently high surface area to ignite OR start with a pre vaporized fuel like propane or butane.


Maybe what you want to build is (the previously mentioned) hotbulb engine, where the hot bulb does the work of fuel vaporization?

That would let you design for a conventional fuel.

Jumping back to the boat in post number two:

Another boat and an older video, but I appreciate what it took to maneuver a small boat powered by one of these:



As someone told me as I drove an unsyschronized stick shift transmission many years ago: "I didn't realize so much manipulation was required."

--ShopShoe

Kegan said:

Any thoughts and ideas?

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George Punter built this Lester a few years back.
Take note of the name as he is a retired secondary school manual arts teacher and winner of the Duke of Edinburgh trophy in the UK so no slouch when it comes to model engineering.

That Lister is not running on Diesel, it is running on model aero engine type fuel. Don't know if George ever got it to work on diesel, it was not the last time I spoke with him

Jasonb said:

That Lister is not running on Diesel, it is running on model aero engine type fuel. Don't know if George ever got it to work on diesel, it was not the last time I spoke with him

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It's still a compression diesel engine with direct injection regardless.
Physics just will not allow it to run on your standard pump diesel fuel, I thought that was obvious.
Seems there is always at least one knocker, apart from the engine that is.

Let me ask, does the small, model diesel engine's diminished mass cause a common inability to create and maintain enough heat within the combustion space to begin the compression ignition process, requiring all true diesel compression ignition model engines to use alternative fuels? Would using a glo-plug be considered cheating?

Bluejets I was just pointing out that the engine in the video was not running diesel fuel but a model engine mix which is what the OP wanted to avoid using and is why he is asking about alternatives.

Glow plugs, hot bulbs, etc would not be cheating if the engine you wanted to model had such a feature. I have the castings for an early Robinson oil engine that will run on Paraffin (Kerro) nothing else added and was what was known as a "permanent lamp" engine which means it always had a blowlamp to keep things hot. Hiding one away may be an option to get an engine running and looking like it is a diesel.

Original engine


Model, some of my pattern work there, just that and mine were cast.

Model "diesel" engines have been around a long time. See https://en.wikipedia.org/wiki/ They run a fuel with equal parts kerosene, ether, and lubricant. Carbureted_compression_ignition_model_engine. Actually even model glow ignition engines are compression ignition that's helped with the glow plug just like smaller diesels when starting.

Lohring Miller

The Ignoble Troll said:

Liquids don't burn, vapours do.

So you are going to either need the engine to have enough heat mass to convert an incoming fuel to vapour OR stick with an atomizer that breaks the fuel into small enough droplets that they have sufficiently high surface area to ignite

Click to expand...

May I ask, as the injectors ports in modern, full-size diesels are small enough to atomize very well, then would a small, model true diesel engine require even smaller orifices and perhaps higher injection pressures to atomize to a proportionately smaller fuel particulate size? Can the fuel be pre-heated to promote vaporization in true, compression ignition?

Klrskies said:

May I ask, as the injectors ports in modern, full-size diesels are small enough to atomize very well, then would a small, model true diesel engine require even smaller orifices and perhaps higher injection pressures to atomize to a proportionately smaller fuel particulate size? Can the fuel be pre-heated to promote vaporization in true, compression ignition?

Click to expand...

It might come down to a lower viscosity fuel with a lower boiling point and a greatly reduced resistance to thermal auto ignition, like n-Heptane... but I am just guessing sorry.

Diesel is classified as a hydraulic oil and as such the injector is a hydraulic pump. So what ever the fuel is, you would need it to promote high pressure lubrication in the injector.

Maybe a hybrid fuel?

A quick reminder- in the last or next to last issue of SIC magazine a Dutch(?) builder ran an article on building a diesel engine he called the "DUX". I remember his discussion of the injector jet as a scribed line down the side of a tight fitting cylinder.

Vietti said:

A quick reminder- in the last or next to last issue of SIC magazine a Dutch(?) builder ran an article on building a diesel engine he called the "DUX". I remember his discussion of the injector jet as a scribed line down the side of a tight fitting cylinder.

Click to expand...

That would be a tiny injection orifice, but how would it ever close? Maybe he just relied on whatever supplied fuel pressure to control fuel flow?
I wonder how much difference there is in power and efficiency between a true compression ignition diesel model engine when running on an alternative fuel -vs- a model hot bulb or similar engine running on actual diesel fuel?

ShopShoe said:

Jumping back to the boat in post number two:

Another boat and an older video, but I appreciate what it took to maneuver a small boat powered by one of these:



As someone told me as I drove an unsyschronized stick shift transmission many years ago: "I didn't realize so much manipulation was required."

--ShopShoe

Click to expand...

The Wichman semidiesel engine has turnable propeller blades to drive forward and backward. Also not transmission gear box.

This fishing cutter is shown in the film was taken in Bergen where I live there.

Kegan said:

I am very interested in diesel engines. I have read multiple articles on true diesels needing atomization of the fuel and very high pressures to ignite. Then I have read articles on compression ignition with fuels like ether that combust at lower pressures but the fuel is hard to come by because of legalities and lack of interest etc. I want to build a compression ignition engines. Stationary horizontal type engines. I am planing on doing a few steam engines first, possibly a few hit and miss types. I eventually want to build a replica of an engine that my uncle had on his farm, a National Gas and Oil engine. I am just wondering what other easily come by fuels are there that can be used instead which don't need to be atomized and don't require such high pressures.

Any thoughts and ideas?

Thank you

Click to expand...

The reason fuels are atomized is because in order to get enough fuel into the cylinder the small droplets allow an increase mas flow with the air mixture. Vapor alone will not allow enough fuel to be atomized. Once under increased pressure and temperature combustion will occur. Above about a compression ratio of 11/1 most hydrocarbon fuels will ignite spontaneously except for the heavier hydrocarbons. Fuels suitable for atomizing work well at lower compression ratios but are not candidates for high compression. The mathematics for the otto cycle indicate that the efficiency is directly proportional to the compression ratio. The math is slightly different for diesels but the higher compression requires fuels that can be controlled at higher pressures. Engines are built for the fuels they will use. Steam engines are a bit different but the boilers are built for the fuels they will use. So a great deal of attention is given to heat transfer area and furnace volume. Most modern diesels by their nature require injectors although they can be designed without them. So the point is you have to identify the fuel, its heat content, its state properties and design an engine to use it.

There are no easily come by fuels, except maybe alcohols and vegetable and plant oils. And even these require preparation. And one more point from a design stand point no matter what fuel you choose it has to have a delivery system.

For your project I would start with a vegetable oil they are known to work well with diesels.

HMEL said:

For your project I would start with a vegetable oil they are known to work well with diesels.

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Alcohol esters work excellent but straight plant oils contain glycerine which is always looking for the chance to become tar or burnt black crunchy stuff.

If you want to go the route of vegetable oil, I would etholate or metholate it. This also reduces viscosity.

We started making patterns for a small replica of Diesel’s first experimental engine earlier this year. Several weeks ago I was hit by a stroke which initially paralysed my right side but now just affects my arm and hand. Hopefully as time progresses I will gain more use and be able to finish it.

We intend to use direct injection rather than air blast and have had some wonderful advice from Roger B over at MEM.

Some 25 years ago I built a 1/4 scale replica of a 2-1/2 HP Hornsby Akroyd oil engine. The engine wasn’t a particularly good runner so rather than have disappointed customers I shelved the project. Only 2 were built. I had no problem making either the high pressure oil pump or the injector. ( other than needing a little magnification )

Cheers Graham.

Klrskies said:

Let me ask, does the small, model diesel engine's diminished mass cause a common inability to create and maintain enough heat within the combustion space to begin the compression ignition process, requiring all true diesel compression ignition model engines to use alternative fuels? Would using a glo-plug be considered cheating?

Click to expand...

Low surface area to volume ratio is definitely an issue. Heat loss rates are higher relative to the total amount of air.

Likely more an issue for cold starts than once the engine gets going.