2 strokes engines, reborn?

To explain the 2 stroke engines is wikipedia. (To remind is interesting read that post).

The big difference with 4 stroke is the scavenging for refill the cylinder very fast, and is more efficiency into the mechanics point of view, due to if no necessary lost energy to move one cylinder one turn without it works. The advantage for 4 strokes is the thermodynamic is easier to manage and more wide rpm band to works.

The big problem of  2 strokes is the contamination, and in the next world more green and with less emissions, the 2 stroke doesn't have gap.

In Europe, the engines needs  satisfy the European emission standards, and it knows like Euro regulations. (Now it goes by Euro 6).

The problem of this engine is the mixture fuel/oil, where we want burn fuel, but the problem is burning oil too. 

Two stroke cycle flows

• First problem is need use the crankcase to compress the air/fuel flow and this enter in the cylinder, and it must carry oil to lubricate the moving parts, the problem is the part of this oil enter in the cylinder and it burn with fuel.
• Second problem is the noise, the exhaust pipe needs a expansion chamber, that this is used in the exhaust pipe, and this provide volumetric efficiency. (The problem is it works only in a rpm narrow band).

The first problem try to resolve with other designs, that they are used in old two stroke diesel engines to locomotives such as Uniflow engine and Stepped engines, and mitigate the second problem.

Stepped engines

I show one image that it is very explicative.

This type engine is used in UAS airplanes

One piston is double, one part  provide air/fuel compress to other part that it is burn cylinder.

The problems is the weight of  piston that it is very big and this is a lot of kinetic energy to high rpm.

Uniflow engine

The uniflow engine used one compressor to scavenging.

Diesel engine Series 71 and 110 by General Motors 

Future two stroke engine

In 2015 we see Kawasaki released the H2 motorcycle

If the used this kind of supercharger plus uniflow scavenging we can use to refill the cylinder.

The advantages are:

1. We don't  pass to crankcase, and no use fuel/oil mixture, this provide cleaner emissions.
2. The second part is no necessary the escape/expansion chamber, due to the pressure of air inlet, provide a fast refill.
3. The supercharger link to crankshaft, it increases pressure and scaveniging time is less, therefore increase the rpm band where the engine works with efficiency.

But is not all perfect, and the disavanteges are: 

1. The injection pressure, of put injection before the supercharger, with the problems the one detonation, or direct injection in the combustion chamber, (it is expensive). In other post I show like put a injection after of supercharger, and eliminate the problems of pressure ;).
2. Supercharger is additional part and the have any problems of lubricants, but the industries have a lot of experience now and these problems could be assume.
3. Limits of speed flows, the air has one limit into the pipes, and this is the sonic speed.

In the other post puts how solutionate the injection problem, but this a problem with all supercharger engines.