Essay #1 Draft

Although two stroke boat motors are considered dirty as far as exhaust emissions are concerned, they are excellent motors because they are powerful, reliable, and economical to operate. Ole Evinrude invented the first outboard motor in 1909. Dugald Clerk is credited for inventing the two stroke cycle engine around 1880. Two stroke engines complete the thermodynamic cycle in two strokes of the piston instead of four. A four stroke engine uses an intake stroke, compression stroke, power stroke and exhaust stroke. A two cycle engine uses the beginning of the compression stroke for the intake and the end of the combustion stroke to accomplish the exhaust function. this allows a power stroke every time the piston goes down instead of every other stroke. This also allows a two stroke engine to have less moving parts and no crankcase oil other than whats mixed with the fuel. Two stroke engines have a high power to weight ratio because they have fewer parts such as no camshafts or valves. There are many different designs of two stroke engines but the most common for outboard motors is the reed valve. The reed valve is a type of one way check valve in the intake port to keep the fuel charge in the crankcase. The newest outboards use direct injection. Oil is injected in the intake port after the reed valve to lubricate the rotating assembly and fuel is injected directly into the cylinder. Direct injection gives more power with less fuel consumption and greatly reduced emissions.
According to the Environmental Protection Agency, non direct injected two strokes can discharge as much as thirty percent of there fuel and oil unburned into the water. The EPA also states that an older seventy horsepower two stroke engine emits as much hydrocarbons as a modern car will in five thousand miles of driving. The San Diego Earth Times estimates that seventy five percent of all motorized boats are powered by two stroke motors. According to Evinrude there new E-TEC two stroke engines are cleaner than most four strokes and currently pass all emissions requirements including California's very strict regulations. Evinrude claims that a fifty horsepower E-TEC will only use two quarts of oil per year in average use.
I currently own an old 1981 Johnson sixty horsepower engine with a jet drive on my flat bottom river boat. The power is adequate for the boat and I can run this combination in about five inches of water. If I were to switch to a four stroke motor I would probably need at least a seventy five horsepower engine to compensate for the weight gain with the four stroke. As far as oil consumption is concerned I mix fifteen ounces of oil per five and a half gallons of fuel. I can run my boat for most of the day on less than ten gallons of gas.
As you can see two stroke motors have been around for a long time and with current technology they are not going away any time soon for the reasons listed above.