Supercharged two stroke?

Look forward to seeing it…

Would sound evil…grins…

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.

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

Ian S C

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

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.

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

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

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

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

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.