25 thoughts on “Diesel, Two Stroke Engine Primer.”
Hrrrmmmmmm.
So my question is – why? The argument for two cycle engines, that I have always seen – is the superior power to weight ratio – and that comes at a cost of decreased fuel efficiency. Yet on this engine we see a heavy gear pump instead of a normally aspirated carb. What am I missing here, Cederq?
What you are seeing is a mechanical, pressurized Roots type blower. Diesels do not use a carburetor, they use injectors
Hmmmmmm. Back in the 50s a lot of the little RC engines were diesel. I’ve never seen one up close and can’t figure them out either… they don’t have blowers or injectors…but there’s some kind of gizmo on the top of the cylinder head the guys fiddle with to get them to run right…
Actually, most 2cy diesels *do* use carburetors…. and don’t burn deisel fuel. The old “cox” model airplane engines are 2cy deisels. No injectors, *and* NO exhaust valves… exhaust ports out the side of the piston.
To be a diesel engine, it just has to use the heat of compression to cause ignition. Obviously you have to use injectors if you want any control over ignition timing, but you can give that up in favor of simpler design, and lighter weight, at the cost of lower efficiency. Big deal if you have to carry it, or if it has to fly.
Yep. The Cox were 2 stroke. They used a sort of reed valve arrangement if my memory desserts me correctly. The flywheel effect of the prop played a significant role in their operation. I like small two strokes. Simple. Get an oil change with every tank of fuel. Screw this green crap. Use it up. Burn it out. Blow it up. Take that, Greta!
The “oil in the fuel” thing is mostly not diesels. Chainsaw engines burn gasoline, use a carburetor, and a spark plug, but there’s no “blower”, they use a sealed crankcase and the vaccuum created there by the rising piston to pull air through the carburetor, then the falling piston pushed it through a cylinder port into the combustion chamber. (I erroneously mentioned a port in the piston, when I should have said the cylinder) This puts fuel/air in the crankcase, so the fuel must also be the lubricant.
Yeah but they are burning nitromethane, right? We call them “glow” engines because they use a glow plug to get them started.
Some of the vintage cool kids refer to them specifically as ‘diesel engines’ and I am confused. Are they burning diesel or nitromethane?
I will have to make inquiries!
Glen, I think they call them diesels because compression is the ignition of the air/fuel mixture and that is a definition of a diesel engine…
Yes you are all correct. Forgive me – I have to do all my own fact checking regardless of the topic. It’s become habitual, I’m afraid….
That’s the only way. Always was.
Truth is the source of authority. Authority is *not* the source of truth.
Two strokes? You listen up y’all and listen good, my Deathray may gets him all excited whens I visit, but his Tank Girl knows how to settle a man down to an even pace.
Johno, go back to bed. And it is getting a little old…
Hey, I’m amusing myself here. How long did I give you the shits with that Hillary stuff?
Deathray is a big boy, who enjoyed multiple first strikes, equally juvenile, without retaliation BTW. I can’t go back to bed, as I cannot leave it in the first place.
Get well, Mr. Johno. Happy New Year!
All he needs is two strokes?
That is all Johno needs…
My cousin had a Detroit on his tiling machine and I could tell where he was anywhere within four miles if the wind was right. Screaming meemie and hell to work next to it.
I do love when a big Detroit diesel marine engine runs away. Keeps me in busines.
My uncle Roy had a big 1950s Lister donkey engine hooked up to a generator to power his house, many miles from the mains electricity power grid. Over a few decades that bastard broke three different forearms when the crank handle kicked back after closing of the decompression lever. I was too quick for it.
The exhaust system fed directly into a below-ground expansion box, so it never annoyed people, no matter how still the day. My uncle would start it around 14.00 and run it until 22.00 hours, for the fridge and freezer.
He was a bushie from way back, so that was the height of easy living for him. The only hassle for him was having to bleed air from the fuel system, if somebody was too slow to refill the fuel tank when it got low.
My memory is of living on a hill South of Edinburgh which was regularly used by Commer two-strokes on their way to a nearby sandpit. Luckily when they were loaded we were on the downhill stretch and so didn’t end up deaf!
Alright some thermo classes for you! Gasoline engine is constant volume heat addition, diesel is constant pressure heat addition. Diesel has the fuel added when the heat of compression is great enough to ignite the fuel, hence high pressure fuel injectors. The more air (O2) in the cylinder, the more fuel that can be efficiently burned. So mechanical/waste heat driven compressors are added upstream to increase charge density. The 16V92’s that drove the generators in the Stewart and Stevenson gensets were both roots and turbo blown.
As an aside the picture is incorrect as there would not be a second inlet to atmosphere. The blower would vent to that side and not efficiently charge the cylinder.
Some small side notes, no spark plugs and diesel fuel has a cetane rating. You want a controlled burn at constant pressure not an explosion when the fuel is injected.
Spin
BSME Minnesota, last century
I always liked Detroit diesels. Seemed to have excessive blowby from road draft tubes, but reliable. Sounded like they going million mph. I not know for sure but suspect turbo on them furnished extra cooling air after injectors were turned up. Good old days…
Most diesel electric locomotives are two stroke. I used to work for Wabtec. The facility where I worked rebuilt the blowers and valve trains for the engines, in addition to a lot of other non-engine locomotive equipment.
Fascinating…. thank you!
The strength of any 2 stroke engine is RPM rather than torque. They are typically used where some kind of pump is being turned. A lot of fire trucks are actually 2 stroke diesels because the main use of the engine is turning a big centrifugal pump and using it to get to the fire is secondary. That’s why some fire trucks sound the way they do. One of my favorite engines of all time is the 2 stroke diesel stationary radial engine. https://en.wikipedia.org/wiki/Two-stroke_diesel_engine
Hrrrmmmmmm.
So my question is – why? The argument for two cycle engines, that I have always seen – is the superior power to weight ratio – and that comes at a cost of decreased fuel efficiency. Yet on this engine we see a heavy gear pump instead of a normally aspirated carb. What am I missing here, Cederq?
What you are seeing is a mechanical, pressurized Roots type blower. Diesels do not use a carburetor, they use injectors
Hmmmmmm. Back in the 50s a lot of the little RC engines were diesel. I’ve never seen one up close and can’t figure them out either… they don’t have blowers or injectors…but there’s some kind of gizmo on the top of the cylinder head the guys fiddle with to get them to run right…
Actually, most 2cy diesels *do* use carburetors…. and don’t burn deisel fuel. The old “cox” model airplane engines are 2cy deisels. No injectors, *and* NO exhaust valves… exhaust ports out the side of the piston.
To be a diesel engine, it just has to use the heat of compression to cause ignition. Obviously you have to use injectors if you want any control over ignition timing, but you can give that up in favor of simpler design, and lighter weight, at the cost of lower efficiency. Big deal if you have to carry it, or if it has to fly.
Yep. The Cox were 2 stroke. They used a sort of reed valve arrangement if my memory desserts me correctly. The flywheel effect of the prop played a significant role in their operation. I like small two strokes. Simple. Get an oil change with every tank of fuel. Screw this green crap. Use it up. Burn it out. Blow it up. Take that, Greta!
The “oil in the fuel” thing is mostly not diesels. Chainsaw engines burn gasoline, use a carburetor, and a spark plug, but there’s no “blower”, they use a sealed crankcase and the vaccuum created there by the rising piston to pull air through the carburetor, then the falling piston pushed it through a cylinder port into the combustion chamber. (I erroneously mentioned a port in the piston, when I should have said the cylinder) This puts fuel/air in the crankcase, so the fuel must also be the lubricant.
Yeah but they are burning nitromethane, right? We call them “glow” engines because they use a glow plug to get them started.
Some of the vintage cool kids refer to them specifically as ‘diesel engines’ and I am confused. Are they burning diesel or nitromethane?
I will have to make inquiries!
Glen, I think they call them diesels because compression is the ignition of the air/fuel mixture and that is a definition of a diesel engine…
Yes you are all correct. Forgive me – I have to do all my own fact checking regardless of the topic. It’s become habitual, I’m afraid….
That’s the only way. Always was.
Truth is the source of authority. Authority is *not* the source of truth.
Two strokes? You listen up y’all and listen good, my Deathray may gets him all excited whens I visit, but his Tank Girl knows how to settle a man down to an even pace.
Johno, go back to bed. And it is getting a little old…
Hey, I’m amusing myself here. How long did I give you the shits with that Hillary stuff?
Deathray is a big boy, who enjoyed multiple first strikes, equally juvenile, without retaliation BTW. I can’t go back to bed, as I cannot leave it in the first place.
Get well, Mr. Johno. Happy New Year!
All he needs is two strokes?
That is all Johno needs…
My cousin had a Detroit on his tiling machine and I could tell where he was anywhere within four miles if the wind was right. Screaming meemie and hell to work next to it.
I do love when a big Detroit diesel marine engine runs away. Keeps me in busines.
My uncle Roy had a big 1950s Lister donkey engine hooked up to a generator to power his house, many miles from the mains electricity power grid. Over a few decades that bastard broke three different forearms when the crank handle kicked back after closing of the decompression lever. I was too quick for it.
The exhaust system fed directly into a below-ground expansion box, so it never annoyed people, no matter how still the day. My uncle would start it around 14.00 and run it until 22.00 hours, for the fridge and freezer.
He was a bushie from way back, so that was the height of easy living for him. The only hassle for him was having to bleed air from the fuel system, if somebody was too slow to refill the fuel tank when it got low.
My memory is of living on a hill South of Edinburgh which was regularly used by Commer two-strokes on their way to a nearby sandpit. Luckily when they were loaded we were on the downhill stretch and so didn’t end up deaf!
Alright some thermo classes for you! Gasoline engine is constant volume heat addition, diesel is constant pressure heat addition. Diesel has the fuel added when the heat of compression is great enough to ignite the fuel, hence high pressure fuel injectors. The more air (O2) in the cylinder, the more fuel that can be efficiently burned. So mechanical/waste heat driven compressors are added upstream to increase charge density. The 16V92’s that drove the generators in the Stewart and Stevenson gensets were both roots and turbo blown.
As an aside the picture is incorrect as there would not be a second inlet to atmosphere. The blower would vent to that side and not efficiently charge the cylinder.
Some small side notes, no spark plugs and diesel fuel has a cetane rating. You want a controlled burn at constant pressure not an explosion when the fuel is injected.
Spin
BSME Minnesota, last century
I always liked Detroit diesels. Seemed to have excessive blowby from road draft tubes, but reliable. Sounded like they going million mph. I not know for sure but suspect turbo on them furnished extra cooling air after injectors were turned up. Good old days…
Most diesel electric locomotives are two stroke. I used to work for Wabtec. The facility where I worked rebuilt the blowers and valve trains for the engines, in addition to a lot of other non-engine locomotive equipment.
Fascinating…. thank you!
The strength of any 2 stroke engine is RPM rather than torque. They are typically used where some kind of pump is being turned. A lot of fire trucks are actually 2 stroke diesels because the main use of the engine is turning a big centrifugal pump and using it to get to the fire is secondary. That’s why some fire trucks sound the way they do. One of my favorite engines of all time is the 2 stroke diesel stationary radial engine. https://en.wikipedia.org/wiki/Two-stroke_diesel_engine