supercharged V12 2 stroke

[dean clarke 2Participant @deanclarke2]

hi guys ,just thought i'd let you all know of my latest attempt at this model engine building lark. Am just in the process of making a supercharged v 12 2 stroke and will try and post photos as i complete bits etc.

dean

[dean clarke 2Participant @deanclarke2]

Methanol burning beast!!

[jason udallParticipant @jasonudall57142]

Supercharged two stroke?

Look forward to seeing it…

Would sound evil…grins…

[HomeUseParticipant @homeuse]

? Is this by increasing the pressure into the crankcase or by increasing the flow between "primary compression" and the main (explosion) compression – keep us posted

[dean clarke 2Participant @deanclarke2]

here is the first stage of the block.

[Raymond FairfieldParticipant @raymondfairfield75804]

Refer to Rolls Royce work at end of WWII. Around 27 litres of it would have been something. Problems with oiling/cooling and superseded by jets.

Ray Fairfield

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

Supercharging the 2 stroke engine is not possible due the inlet port and exhaust port is still open and zero effective cylinder filling. Also the pressure of fuel/air in crankcase is trowing away out of exhaust port. To make the 2 stroke engine effective: Use tuned pipe.

[DerryUKParticipant @derryuk]

IIRC when MotoGP switched to four-strokes the two-stroke bikes were producing 360 BHP/ltr.

[Ian S CParticipant @iansc]

Rather than a supercharger, a two stroke would have a scavenging pump. Sounds like a interesting engine.

Ian S C

[jonathan heppelParticipant @jonathanheppel43280]

Some 40 years ago there was a series in ME titled " Blower charged two stroke engines", if memory serves. The author firstly experimented with a vertical twin, then built a rather pretty V4.

[Martin WParticipant @martinw]

Hi Dean

While on a somewhat different scale two stroke turbo charged diesel engines are used to power some of the larger ships today, see this link.That said I have no idea how this would be implemented on a small scale!!.

Cheers

Martin

PS

That's an impressive group of engines you have displayed in your album

Edited By Martin W on 07/12/2013 11:18:29

[Ady1Participant @ady1]

The RTA96C-14 turbocharged two-stroke diesel engine is produced by Swiss company Wartsila-Sulzer and is the largest and most powerful diesel engine in the world today.

A Swiss Company…. Switzerland is landlocked and produces marine diesels…

Whatever happened to Britannia rules the waves?

[Clive HartlandParticipant @clivehartland94829]

The engine that powers Greyhound Buses and the M109 is a 2 stroke diesel and is double supercharged. It has a Rootes blower and an exhaust blower.

The space between the V cylinders is a Plenum chamber, the Rootes blower sits above it and the exhaust blower feeds the Rootes blower. The cylinder sleeves have a 360 deg. porting and I would assume the blowers just overpressure the cyl. to evacuate the exhaust?

The exhaust type is a parallel double tube with one end closed off and helps blow out exhaust gases. In fact my SAAB 95 had such a system in the exhaust, very efficient.

I can see supercharging before the fuel inlet as a method, that I am sure would work. I wonder what is the point as I have had McCoys and Doolings peaking at 20000 + rpm and these were single cyl.

We had an incident where an M109 engine, 'ran away' and to stop it a certain Snco bunged his combat jacket into the inlet to the superchager and it very kindly sucked it in and shredded it into fluff and bits of zipper. It barely coughed while doing! The Injectors where the pump type and on a rail and the linkage would jam and thats why it ran away.

[V8EngParticipant @v8eng]

I seem to remember from my youth that some Commer lorries were fitted with blown 3 cylinder 2 stroke engines.

No idea how it was all arranged, but the sound was very unusual.

Edited By V8Eng on 07/12/2013 12:59:48

[V8EngParticipant @v8eng]

Oh yes nearly forgot to mention the wonderful Deltic 2 strokes but they were Turbocharged, which sounds pretty much well suited for the application.

your engines look very good dean, I look forwards to seeing this one progress.

Edited By V8Eng on 07/12/2013 14:07:45

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

The supercharger in the two stoke engine is not same as a 4 stroke engine with super charger when we are speaking about increase the horsepower out of the engine. In the large 2 stroke engine such as in Sulzer or in Messerscmitt, these large engines is without crankcase as a blower as in all small 2 stroke engines do have it, hence the supercarger/Rootes blower is used as a blower while the moving parts below the piston/cylinder is lubricated by circulation oil.

[JAParticipant @ja]

Posted by Raymond Fairfield on 07/12/2013 05:50:11:

Refer to Rolls Royce work at end of WWII. Around 27 litres of it would have been something. Problems with oiling/cooling and superseded by jets.

Ray Fairfield

The RR Crecy was complex even by the standards of aeroengine engine design towards the end of War. In its full form it was a V12 two stroke with a typical RR engine driven supercharger. It used sleeve valves with only inlet ports, the gases exhausted over the top of the sleeve. The fuel was injected directly into the engine. Thankfully the jet engine arrived.

Rolls-Royce Heritage Trust publish an excellent book of sectioned drawings of piston aeroengines which includes the Crecy and Junker Jumo, a typical opposed piston diesel engine similar to the Roots engine except that it had two crankshafts.

JA

[Ian AbbottParticipant @ianabbott31222]

What Clive is on about is the General Motors 8V92. A turbo on each bank of the V8 feed a roots blower in the V. Intake is via ports in the cylinder walls and exhaust is through two normal poppet valves in the head. There's no injection pump, each cylinder has its own, camshaft driven via push rods. They're notorious for running away, so there's a panic flap on the intake, with a red knob in the cab to pull. It doesn't stop the engine, but it does give you time to select a high gear to try to stall it. It's truly frightening when one gets away.

A lot of the big trucks in the States and Canada use them, Kenworth et al.

The 8V92 designation is eight cylinders of 92 cubic inch in a V formation. That's (reaches for calculator) 736 cubic inches. About 12 litres, I think.

Ian

[Clive HartlandParticipant @clivehartland94829]

As its some 43 years back since I overhauled these 'V' 2 stroke engines its all coming back to me. They had 4 valves per Cyl. and a pump injector driven off the cam shaft that also operated the valves. The supercharge pressure was 24lb. The pressure was in the Plenum chamber between the Cyl. and was passed into the bores through the 360 deg porting. So that as the piston was pushed down by burning fuel the valves opened at BDC and the supercharge pressure cleared the cyl. of burnt gases. Valves close and the pressure is then taken up by the pistons and they move up and the pump injects the fuel at TDC and the cycle goes on. the Pistons had a chamber in the crown. I think they were 440bhp and moved the gun through an automatic gearbox and could do 45mph. It weighed 42 Tonne was made of Alu. armour. Hard on the outside and soft inside. From conversations with US crewmen it did not stop RPG. It stopped small arms fire. It was armed with a 0.5 Browning on the cupola hatch. Steered by a wheel not tillers. The Gunners like them and it was a very accurate gun at 155mm bore. I have seen them lob shells down the hatch of target tanks at 2500 meters. Had a range of some 19km. and after we up-gunned them with a longer barrel and a base bleed shell it went out to about 27km.

I believe no longer in service. Clive

[John OlsenParticipant @johnolsen79199]

DKW had a supercharged two stroke petrol motorcycle before the war. I beleive the supercharger was a piston type, and the supercharge was applied before the crankcase compression. I beleive the power cylinder or maybe cylinders, was a split single design which allows assymetrical timing for the transfer and exhaust, which would be desirable since otherwise most of the mixture would just blow on through. As it was, I gather the fuel economy was terrible, about three miles to the gallon. The link says that when they reaced in the Isle of Man you could hear them 60 miles away on hte mainland….

**LINK**

John

[dean clarke 2Participant @deanclarke2]

hi again, thanks for the info. i believe that it is possible to supercharge 2 stroke engines. the object of the super charger is to create a crankcase pressure when it is unable to be used as a pump eg there is more than 1 piston in a common crankcase which therefor removes the ability of the crankcase to be a pump for the transfer. so add 1 blower and problem solved. there are many commercial engines that have been built to this design over the years. the berger 7 cylinder 2 stroke radial is just 1 example that springs to mind.

will update photos tonight as the crankcase is now finished

dean

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

Here is text about crank case compresion and supercharging in 2 stroke engine..

**LINK**

"This is clearly impossible in normal two-strokes in which exhaust and ports are open simultaneously. They can, however, be "super-scavenged" by an oversize charging pump, often with some advantage, but at the expense of economy, because wastage of fuel through the exhaust port is inevitably increased. This may be tolerated in racing engines, and is no disadvantage in diesel engines of the injection type, which are charged with air only. In my experiments, however, I have failed to obtain any substantial increase of performance in two-strokes by increasing the charging pump volume."

Wrote by E. T. Westbury

[John OlsenParticipant @johnolsen79199]

As Mr Westbury said, you can't really get any supercharge on a conventional two stroke, since the exhaust port will usually be open until after the transfer port has closed. So the pressure in the cylinder cannot be higher than the exhaust pressure. The exhaust pressure can of course be made to be high at just the right moment with a suitable tuned pipe, but that will only work over a narrow power band.

The DKW mentioned above is a split single, eg two cylinders with a common combustion space, and both worked off the same crank. This allows assymetrical timing, eg the exhaust opens before the transfer, and then closes before the transfer. That would allow the cylinder to be pressurised by the crankcase pressure, and if there is a blower driving the mixture into the crankcase, supercharge will be acheived. However I think that even with this advantage, a lot of mixture must have just gone straight out the exhaust port before it closed, going by the fuel mileage I have seen quoted.

I guess for a model as per the original post, the convenience of having a common crankcase might make it worth having a separate blower to do the scavenging, and if you don't overdo the crankcase pressure the economy should not be too bad, at least by the usual standards of small engines, which tend to be pretty thirsty. It won't actually be supercharged, unless you can provide for the transfer to close after the exhaust. Some two stroke diesels manage this by having two pistons in one cylinder, inlet controlled by one piston and exhaust by the other. Then by offsetting the cranks a little you can get assymetrical timing.

John

[dean clarke 2Participant @deanclarke2]

here's the finished block only need to do the engine mounting holes. oh and the obvious finishing of the outside surfaces which will be done when all machine work is completed.

will keep you posted

dean

p.s. i hear what your saying about the open exhaust port but there is also a massive valve overlap in all high performance 4 stroke engines that run blowers too, so really it is not that different to a schnurle ported 2 stroke

[Gordon WParticipant @gordonw]

Can't remember who, but a well known engine designer once called a racing 2 stroke " a mobile petrol cooled exaust system " Sorry to be a bit off topic.

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