2 Stroke Engines...

This post continues by highlighting the differences between a 2 and 4 stroke engines and discusses some of the issues with 2 stroke motors.

As I mentioned earlier we were discussing the standard internal combustion engine.  There are several engine designs but we discussed the easiest to understand.  I will talk about another engines that come to mind.  The engine I previously talked about is called a four-cycle engine.  But there is a variation of this engine and it looks about the same in physical shape but the way it handles fuel intake and exhaust are very different.  This engine is called a two-cycle engine or sometimes referred to as a two-stroke engine. It is used where weight and size are of primary importance. It is used on chain saws, outboard motors, inexpensive lawnmowers, weed wackers, leafblowers, some motorcycles, snowmobiles, water jet skis and model airplanes motors. 
    Today in the United States most of these usages of the two-stroke motor have been legislated against due to air and water pollution. It is still a standard on chainsaws, leaf blowers and weed wackers.  Even the model plane hobby enthusiast is using small four-cycle engines. The two-stroke engine has more power per pound then four-stroke engines but has two major drawbacks.  First it waste fuel and second is the smoke it produces, which is air pollution.
    I will start by explaining the strokes of this engine.  Remember the four-stroke engine is intake, compression, power and exhaust.  The two-stroke engine has just two cycles, compression and power. We must visualize a piston going up and down in a closed chamber or cylinder. This cylinder must have passages to allow the fuel to get in to the combustion chamber and passages to allow the exhaust to leave the combustion chamber after it has been exploded. 
    On this engine, no cycle can support itself.  While the piston is traveling up it is creating a vacuum under the piston and sucks in fuel and air into a closed crankcase. This mixture is pushed into the combustion chamber when the piston is traveling down by the exploding of fuel in the combustion chamber. While traveling down the piston uncovers holes in the cylinder, which are called ports, to let the exhaust go out.  Now this downward motion of the piston pushes the fuel and air mixture into the combustion chamber where it is exploded again and the cycles continue.
    I could list many ways that the engine controls the opening of the passages that let in the fuel and air mixture and then let the exhaust out.  Some engines have a rotary valve, some have a reed system, while some have matching holes in the piston and cylinder. Some engines have a exhaust valve to let the exhaust out. 
    Now for the reasons that the two stroke engine is not widely used for transportation. The fuel efficiency is poor. In order to push the exhaust out while fuel and air are being pushed in, it is necessary to allow some of the fuel mixture to go out with the exhaust. This is air pollution.  Another reason for its inefficiency is that the two-stroke engine needs to have oil added to the fuel to lubricate the working parts of the engine, such as the bearings and piston. After the oil lubricates the working parts of the engine it is then burned up and the result is smoke and smell.  On outboard motors(such as used on a fishing boat), the oil that does not make it to the combustion chamber to be burned, is collected and pumped in to the water. This creates an oil slick on the water.  Some lakes that are used for drinking water have outlawed the use of two-stroke outboard motors for this reason. This also is true for jet skis and they are now being outlawed on many lakes. 
    Because of the waste of oil and the air pollution, oil to fuel ratios have been improved in two-stroke motors. Early ratios were 16 to 1, that is 16 parts fuel to 1 part oil.  As better oil was invented, the ratio was improved and is now up to 100 to 1. To eliminate owner error, oil was dyed to a red or blue color to allow the user to see that oil was in the fuel. Then oil injection was invented, that is oil is stored in a separate tank and pumped into the engine in a metered amount to help solve operator error and air pollution.
    Oil also came in three varieties, mineral, vegetable and man made. Mineral oil is pumped from the ground and refined. Vegetable is oil extracted from the caster bean and it smells the best. Man made oil, or synthetic oil - lubricates the best and is used in the 100 to 1 ratio. While writing this article I can remember engines that I have worked on - some so small that I could hold the engine in the palm of my hand and some so big that I used a hoist to lift it up to bolt it on the back of a boat.