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What is a Diesel Engine ?
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peterl95124
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Roger, thanks!, I found the F1 article very interesting! (but its still spark-ignition), but the HCCI article is about how model airplane diesel engines have always worked and is neither interesting nor promising IMHO its just another unnecessary research project, YMMV...
Pete.
Roger B
Well-Known Member
All these developments are derivatives, the TJI can be seen in the HVID ‘diesel’ design as well as the early German Diesel pre combustion chambers that were an attempt to replace the air blast injection.
The HCCI is a valid development if it can do away with the complicated high pressure injection systems and still deliver flexible load and speed control.
Model aircraft ‘diesel’ engines generally run under fixed conditions driving a very benevolent load, a propellor. As the speed drops the load drops. The first model aircraft Diesel engines had fuel injection but the developer, Eisfeld, found he could get similar results with carburation.
A further development was the Lohmann 18cc ‘diesel’ moped. This was able to deliver flexible load and speed but required the operator to adjust the fuel mixture and compression ratio accordingly.
https://onlinebicyclemuseum.co.uk/1951-lohmann-18cc-diesel-engine-new-old-stock-unused/
The HCCI development work is using different techniques, such as exhaust gas recirculation and pre heating of the intake air/mixture to obtain flexibility. I wait to see if it will eventually offer a cheaper engine with improved emissions.
The HCCI is a valid development if it can do away with the complicated high pressure injection systems and still deliver flexible load and speed control.
Model aircraft ‘diesel’ engines generally run under fixed conditions driving a very benevolent load, a propellor. As the speed drops the load drops. The first model aircraft Diesel engines had fuel injection but the developer, Eisfeld, found he could get similar results with carburation.
A further development was the Lohmann 18cc ‘diesel’ moped. This was able to deliver flexible load and speed but required the operator to adjust the fuel mixture and compression ratio accordingly.
https://onlinebicyclemuseum.co.uk/1951-lohmann-18cc-diesel-engine-new-old-stock-unused/
The HCCI development work is using different techniques, such as exhaust gas recirculation and pre heating of the intake air/mixture to obtain flexibility. I wait to see if it will eventually offer a cheaper engine with improved emissions.
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The ideal with HCCI is to have a cool, lean burn. Lean burn like a diesel is ideal for fuel economy, but the combustion of a diesel is very hot around the fuel droplets hence excessive NOx emissions, and also the burn conditions can be rich in some areas of the cylinder at high loads (= black smoke). If you can manage to ignite a lean homogeneous charge it burns slowly and at comparatively low temperature, with minimal emissions. The challenge is doing that in a controllable fashion. Mazda with their skyactiv-X design managed a kinda-sorta version by using a small region of normal spark ignition combustion to compress the lean homogeneous charge to ignition. But it doesn't seem to have been much of an improvement on a modern spark ignition engine.
Hi Lloyd: re: "pour some gas on a rag and hold it over the diesel air intake." - I had forgotten the mechanic did that when I was a kid to get a diesel engine started..
Nostalgia of a Saturday morning job at a machine shop....
I remembered it once on a VAN with a diesel, where the battery was a bit tired and the glow-plugs didn't automatically switch ON with ignition ON... before cranking. We had run out of "Easi-start". but we had some paint solvents handy, and splashed some on the air filter, fitted it and started the engine. Went like a racer for a half minute until the fumes had all been consumed - then was fine.
Fixed the flat battery and glow-plug relay and never needed that again.
K2
Nostalgia of a Saturday morning job at a machine shop....
I remembered it once on a VAN with a diesel, where the battery was a bit tired and the glow-plugs didn't automatically switch ON with ignition ON... before cranking. We had run out of "Easi-start". but we had some paint solvents handy, and splashed some on the air filter, fitted it and started the engine. Went like a racer for a half minute until the fumes had all been consumed - then was fine.
Fixed the flat battery and glow-plug relay and never needed that again.
K2
ajoeiam
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Hmmmmmmmmmm - - - might be possible in Chrome - - - - that doesn't happen in Firefox - - - sorry.
Weird, it should. Even works in IE.
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Try right clicking and opening the image in it's own tab?
ajoeiam
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Even then!
(I seem to be considered someone who doesn't have any idea how to maneuver the internet - - been on it since 1986 so that's not true either!)
Only option is to download the image, save it and then use a graphics program to enlarge it.
Problem with that is that the text doesn't necessarily scale well - - - which is why I asked for urls for source docs. (they seem to not be available)
I'm sorry, that was not the vibe I meant to give off. Genuinely made no assumptions on your abilities, the enlarge shortcuts are things lots of people don't know about so I was just trying to help. It's all good.
That is correct. It is the zoom function of the windows operating system.
ajoeiam said:
(I seem to be considered someone who doesn't have any idea how to maneuver the internet - - been on it since 1986 so that's not true either!)
He is just trying to help, no one can know how much you know about the internet and computers.
Here ...Firefox : zoom
Image link :
https://www.homemodelenginemachinis...-2-stroke-will-it-ever-work.31110/post-413561
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rolphill
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I thought I'd add my two cents. First of all, model glow engines are not technically compression ignition. The glow plug wire is plated with platinum, which (when hot) undergoes a catalytic reaction with the nitromethane in the fuel to ignite the charge! The heat from the reaction is enough to maintain the temperature of the platinum wire after starting the engine.
Also, hot bulb engines are super under-rated IMO. A couple years ago I did a TON of research and tried to build one out of a weed whacker engine. I was really interested in trying to make algae bio-diesel and I needed an engine that could burn it.
It was kind-of a quick and dirty side-side project, so I used a solenoid valve, and an electronic control. I tried to fuel it with vegetable oil, and I got exactly two big pops before stinking up the place, getting frustrated, and moving on. It was kind of promising, so I'll probably come back to it at some point. The main issues were minimizing heat transfer from the hot bulb, and minimizing dead space in the hot bulb to keep the compression ratio up.
Also, hot bulb engines are super under-rated IMO. A couple years ago I did a TON of research and tried to build one out of a weed whacker engine. I was really interested in trying to make algae bio-diesel and I needed an engine that could burn it.
It was kind-of a quick and dirty side-side project, so I used a solenoid valve, and an electronic control. I tried to fuel it with vegetable oil, and I got exactly two big pops before stinking up the place, getting frustrated, and moving on. It was kind of promising, so I'll probably come back to it at some point. The main issues were minimizing heat transfer from the hot bulb, and minimizing dead space in the hot bulb to keep the compression ratio up.
Bizarre, but VERY interesting. Do you have more info on this somewhere?
Thanks, Lloyd
Roger B
Well-Known Member
The hot bulb engine had several disadvantages:
The low compression ratio, typically around 5-1 gave a low thermal efficiency compared to the Diesel engine and to the spark ignition engine as higher octane fuels became available.
There is a significant time required to heat up the hot bulb (interestingly you could consider the model glow pug engine as a logical solution to this problem).
The combustion timing is controlled by the geometry of the hot bulb and connecting passage. Optimizing for different fuels requires changing components not just adjusting the ignition or injection timing. The Lanz Bulldog offered a selection of cylinder heads/combustion chambers.
That being said you have an interesting project there. It avoids the need for precise high pressure injection systems as the fuel is injected at the start of the compression stroke not at the end. How did you choose the size of the connecting passage and the volume of the hot bulb?
The low compression ratio, typically around 5-1 gave a low thermal efficiency compared to the Diesel engine and to the spark ignition engine as higher octane fuels became available.
There is a significant time required to heat up the hot bulb (interestingly you could consider the model glow pug engine as a logical solution to this problem).
The combustion timing is controlled by the geometry of the hot bulb and connecting passage. Optimizing for different fuels requires changing components not just adjusting the ignition or injection timing. The Lanz Bulldog offered a selection of cylinder heads/combustion chambers.
That being said you have an interesting project there. It avoids the need for precise high pressure injection systems as the fuel is injected at the start of the compression stroke not at the end. How did you choose the size of the connecting passage and the volume of the hot bulb?
rolphill
Well-Known Member
It was HARD to find technical info on hot bulb engines. Looking through old (30's) magazines online and such. (It was interesting to read an article from 1933 that referred to WW1 as "this great war", they already knew there would be more.)
They came up with all kinds of fancy improvements to the hot bulb engine. (Keep in mind most of these are far more applicable to large boat engines, not so much models.) Most memorable was the spray nozzle in the hot bulb could change the spray pattern. At idle it sprayed in more of a cone or mist. But under heavy load it would spray a straight jet at the opposite wall of the hot bulb to delay ignition. Note that the bulb would be much hotter under heavier load. Also different injection locations, into the bulb vs at the piston head.
An oft remarked advantage of hot bulb engines was that they were far more tolerant of dirty fuel, due to looser injector tolerances. Also the big ones were two stroke, with bearing oil injection pumps not unlike steam engine mechanical pumps. Note that the intake charge is clean air. Notably they would run away for a bit if there was a pool of oil in the sump from a funky bearing lube pump.
I could not find any sort of reliable data on horsepower per liter. Bare minimum compression ratio was probably 3:1.
I suggest that before trying to build an engine from scratch, first try to make a hot bulb that screws in to the sparkplug hole on a lawnmower engine, and start doing experiments.
At small scales, your biggest enemies are heat lost through conduction from the bulb to the engine head, and low compression ratio from the hot bulb and passage dead space. Don't worry about trying to make it run without constant fire on the bulb.
The engine in the picture was a weed whacker engine. I used an rv water pump with built in pressure switch to maintain fuel pressure. The solenoid valve was a special high speed high temp valve, ~12ms open time, ~7ms close time. It was controlled by a one shot circuit with an adjustable pulse length, and triggered by a reed switch off a flywheel magnet.
The hot bulb had a volume of about 3cc including the volume of the tube. I made a couple different ones, the smaller and the less ability to conduct heat to the head the better. This is gonna be really hard to scale down. I don't think the weed whacker engine was gonna work well, too small and designed to run very fast.
Yall make me want to try again! I have an old 12hp Briggs flathead that idles at like 500rpm. I could trigger the valve off the points. I could even make a sealed bulb and inject oil into the intake.
Oh, here's a fun video for you:
They came up with all kinds of fancy improvements to the hot bulb engine. (Keep in mind most of these are far more applicable to large boat engines, not so much models.) Most memorable was the spray nozzle in the hot bulb could change the spray pattern. At idle it sprayed in more of a cone or mist. But under heavy load it would spray a straight jet at the opposite wall of the hot bulb to delay ignition. Note that the bulb would be much hotter under heavier load. Also different injection locations, into the bulb vs at the piston head.
An oft remarked advantage of hot bulb engines was that they were far more tolerant of dirty fuel, due to looser injector tolerances. Also the big ones were two stroke, with bearing oil injection pumps not unlike steam engine mechanical pumps. Note that the intake charge is clean air. Notably they would run away for a bit if there was a pool of oil in the sump from a funky bearing lube pump.
I could not find any sort of reliable data on horsepower per liter. Bare minimum compression ratio was probably 3:1.
I suggest that before trying to build an engine from scratch, first try to make a hot bulb that screws in to the sparkplug hole on a lawnmower engine, and start doing experiments.
At small scales, your biggest enemies are heat lost through conduction from the bulb to the engine head, and low compression ratio from the hot bulb and passage dead space. Don't worry about trying to make it run without constant fire on the bulb.
The engine in the picture was a weed whacker engine. I used an rv water pump with built in pressure switch to maintain fuel pressure. The solenoid valve was a special high speed high temp valve, ~12ms open time, ~7ms close time. It was controlled by a one shot circuit with an adjustable pulse length, and triggered by a reed switch off a flywheel magnet.
The hot bulb had a volume of about 3cc including the volume of the tube. I made a couple different ones, the smaller and the less ability to conduct heat to the head the better. This is gonna be really hard to scale down. I don't think the weed whacker engine was gonna work well, too small and designed to run very fast.
Yall make me want to try again! I have an old 12hp Briggs flathead that idles at like 500rpm. I could trigger the valve off the points. I could even make a sealed bulb and inject oil into the intake.
Oh, here's a fun video for you:
Where you soxhlet extracting your algae or pressing it?
Did you consider pyroligneous tar?
After playing with some Cladophora algae and seeing how much cellulose it produced vs oil, I always wanted to pyrolize it whole and convert it into basically diesel fuel, but I had no engine to test it in.
Algae biodiesel is a funky topic, I know of some researchers in that area who are trying to make algae whose photosynthesis is *less* efficient at absorbing light. The reason being that the algae easily block light from all but the top of the tank, so algae lower down die! Apparently stirring doesn't work because the algae also don't like going from light to dark constantly.
Sounds like a long tank, low and slow feed of clean water one end to flow out the top surface - maybe with a roller to collect the algae - at the other end? I assume the water is oxygenated by the algae? - So would CO2 bubbling at the input help provide the "carbon" for making hydrocarbons using sunlight? A form of Biological sequestration?
What a weird subject I didn't know existed! And you are making a model of an "industrial process"...
Thanks for posting that!
K2
What a weird subject I didn't know existed! And you are making a model of an "industrial process"...
Thanks for posting that!
K2
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