Essay #1 Final Draft

LONG LIVE THE TWO STROKE!

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.

Dugald Clerk is credited for inventing the two stroke cycle engine around 1880. Joseph Day and one of his workmen designed the valve-less two strokes in 1889 which is basically what we use today. Ole Evinrude invented the first outboard motor in 1909.

Outboard motors on boats were developed as a self contained unit to power small boats. They are mounted on the back or stern of the boat. It can be pivoted or turned to steer the boat. They can have a propeller or, what is referred to as a jet unit. A jet unit is a type of enclosed propeller that forces a large amount of water through a small nozzle, or jet to propel the boat. Two stroke engines complete the thermodynamic cycle in two strokes of the piston. A two cycle (two stroke) 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. A two stroke engine has no camshaft or valves, and no crankcase oil other than what’s mixed with the fuel. Two stroke engines have a high power to weight ratio because they have fewer parts.

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 (fuel mixture) in the crankcase. The newest two stroke outboards use direct injection. Oil is injected in the intake port after the reed valve, to lubricate the rotating assembly. The fuel is injected directly into the cylinder. Direct injection gives more power with less fuel consumption and greatly reduced emissions. However there is still controversy over the use of older non-direct injected two stroke motors.

The San Diego Earth Times and the state of California state that according to the Environmental Protection Agency (EPA), non-direct injected two strokes can discharge as much as thirty percent of their fuel and oil unburned into the water. The EPA also states that an older (prior to 1999) seventy horsepower two stroke outboard motor 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 their 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 engine. 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. The basic design has not changed much in one hundred years, proving its reliability. A two stroke motor’s power to weight ratio is unmatched. Two stroke motors are economical because they use very little oil, require no oil and filter changes, and minimal maintenance. Current technology has made two stroke outboard motors clean running, powerful, and fuel efficient.

REFERENCES:

http://www.sdearthtimes.com/et0897/et0897s2.html
http://www.outboardcentral.com/content/view/16/1/
http://en.wikipedia.org/wiki/Two-stroke_engine
http://www.dbw.ca.gov/Environmental/TwoStroke/