Which is Better Two Stroke IC Engine or Four Stroke?

4 stroke....

Or a Wankel Engine?

or a steam engine?

Well this one has the lowest emissions!

or this one

go electric

Go nuclear!!

Go diesel/Electric hybrid.....

"BMW's overarching goal was to combine breath-taking speed and groundbreaking efficiency. In the BMW Vision, that boils down to 4.8-second 0-to-60 miles per hour acceleration and 63 mile to the gallon.

First, BMW engineers use the rear-axle to combine a turbo-charged small diesel engine and the mildest forms of hybrid technology. That kind of combo comes standard in BMW 1-series cars in Europe. The Vision's setup is a little more similar to the BMW 320d, also to debut in Frankfurt, which uses a 2.0-liter four-cylinder diesel to deliver 162 horsepower, while promising more than 57 miles to the gallon. The BMW Vision takes it a step further by downsizing the engine to a 1.5-liter three-cylinder diesel engine mated with the more robust hybrid system found in the pricey BMW ActiveHybrid7, expected in the US early next year.

Not satisfied with 162 horsepower, BMW adds a second motor to drive the front wheels exclusively by electricity. When both motors and the diesel engine are called into service, the overall system can put out 356 horsepower. The BMW Vision is lightweight and aerodynamic. "

Let's not forget about

The search engine.

A two stroke can be pretty darn impressive.

Wärtsilä RT-flex96C an 80,080 kW Diesel engine with 5,608,310 lbf·ft of torque.

Needs a new name.....Like 'King Kong' er somethin'.....Maybe "The Beast"....

'King-Kong' would be a definite improvement over 'Wort-zilla'

To round the picture out, 2 bangers made by Bombardier in the 120 Hp or less range are light and reliable. For snowmobiles, and small light airplanes, etc.

Then there are mostly sub 1Hp ones, frequently used for airplane models.

So, what is it meant for?

The precise answer to the question as asked is, "It depends." And why is the six-stroke engine configuration not even considered (http://en.wikipedia.org/wiki/Six-stroke_engine)? There are literally dozens of parameters which need to be considered before this question can be answered for any real-world situation. With none of the conditions given, no definitive answer is possible beyond, "It depends."

Imagine that the answer did NOT depend upon whether the need is for a tiny, high-revving single cylinder lightweight ICE running on an exotic fuel mixture, or for an enormous, low-speed torque monster to run upon heavy crude oil. Imagine that it didn't matter whether this was to be a one-of-a-kind device, or to be produced in vast numbers at the lowest possible cost. Imagine that expected lifetime, reliability, and repairablility were of no consequence. Imagine that all fuels were equally available at all places, and that costs were equal among them. IF none of these conditions mattered, there would only be one form of internal combustion engine being made, and you would already know the answer; but the conditions under which the engine will be designed, manufactured, and used; the availability of particular fuels at particular locations, and the differing costs at those places, the long-term reliability, cost to manufacture, cost to use over an anticipated lifetime, and MANY other considerations need to be defined prior to improving upon, "It depends."

Define "better".

Fewer moving parts?

Lower exhaust emissions?

Lower weight?

Lower cost?

Power to weight ratio?

Wide operating RPM range?

Low RPM torque?

Ring-ding marbles in a can sound?

The sweet smell of partially burned castor oil?

It all Depends on the Application....

"It all Depends on the Application...."

And even for small propeller-driven aircraft as shown in the picture, there are two- and four-stroke spark ignition engines, diesel and electric motors. Turboprops are only a step larger, and pure jets are used down to single-place sailplanes and home-builts, as well as even SMALLER: http://www.jetman.com/.