don't use gasohol in a 2 cycle engine. It's not good for them in general and if it's his performance it will ruin it. Some 4 stroke engines can use it, but check your manual. Keep it out of hi performance stuff . Generally avoid it if possible. Generally, the purer your fuel, the Better the performance.
no
Two-cycle lawnmower engines are rare.
I think you are looking for a detailed engineering answer. Common usage is that a two stroke engines is called a two stroke engine. By the way my experience says that two stroke engines only have two strokes and the second one is fatal.
yes
Miller Cycle and Boxer. Internal and External.
gasoline & methanol
very large is the keyword here. for a very large engines that runs large machines, we need high power engines. two-strike cycle engines produce more power than 4-stroke cycle engines. that's why they are used. as they produce more pollution than 4-strokes, they must be limited to small spaced engines machines or large machines that required very high power.
cross scavenged engines
Yes, two stroke (or Two cycle) engines have oil that is mixed into the fuel to lubricate the motor's moving parts. Where as, in a 4 stroke engine the oil is separate from the fuel. When the fuel oil mix is burned in a two cycle engine more pollution is given off.
Unless we are talking about big diesels - Yes.
Yes, most chainsaws do have two stroke/cycle engines. However, people have made them with four stroke/cycle engines such as the V-8 chainsaw seen here: http://www.youtube.com/watch?v=60Tamp2fHhg
Two cycle (two Stroke) engines generally have one spark plug per cylinder. So a four cylinder, 2 cycle engine will have 4 spark plugs.