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Old 02-11-2010, 06:19 AM   #1
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How Does a Marine Diesel Work?

You just purchased that stunning used 1985 Vista sundeck trawler and shes everything you needed in a trawler.* The nice sundeck, the owner's quarters and the big fly bridge are perfect.* She's also got twin Volvo diesels and a Onan genset also.* But youve been thinking, how do those engines really work?* These are the first diesels you have owned.

Now you old salts out there probably already know this, but we're talking to the new trawler enthusiast that is looking at his first boat.

In theory, diesel engines and gasoline motors are quite similar. They are both internal combustion engines designed to convert the chemical energy available in fuel into mechanical energy. This mechanized energy pushes pistons up and down inside piston chambers. The pistons are joined to a crankshaft, and the up-and-down motion of the pistons, recognized as linear motion, creates the rotary motion required to turn the prop on your used trawler or motor yacht.

In today's world, where fuel prices are increasing as a outcome of increasing demand and diminishing supply, we must select a cost effective fuel to meet our needs.

Thanks to the invention of Rudolph Diesel in 1892 in Augsburg, Germany, the diesel engine has proved to be exceedingly efficient and cost effective.* In1894 Rudolph Diesel was nearly killed when his engine exploded.* But that explosion established that diesel can be ignited without a spark.

Diesel engines were the first bio-fueled motors.* Diesels first diesel engine ran on peanut oil.* In the real world, a diesel engine can operate on peanut oil, vegetable oils, synthetic oils, and even hydraulic fluids.* Rudolf Diesel even tried out operating earlier diesel engines with gun powder.* Handling and storing of the gun powder soon laid to rest that idea.

When petroleum was found to be a easily obtainable resource, a product we now call diesel fuel was processed to power diesel engines.* Diesel fuel is priced somewhat higher than gasoline but diesel has a greater energy density, i.e. more power can be extracted from diesel as compared with the same amount of gasoline. Therefore, diesel engines furnish greater power, making it an unmistakable choice for big used trawlers and motor yachts. Diesel is heavier and oilier compared with gasoline.* Diesel fuel has a high flash point making storage aboard a boat very safe.

The easiest way to think of how a diesel engine works is by memorizing the phrase "suck, squeeze, bang, and blow". This refers to a cycle of 4 strokes known as the OTTO cycle.

To begin with, air is pulled into the piston chamber (suck). The air is then constricted by the movement of the piston, fuel is then injected as a vapor just before the piston contacts the top of the cylinder (squeeze). This compression raises the temperature of the air; which causes the diesel fuel to combust (bang). Finally, the burned gases are blown from the piston chamber (blow) and into the exhaust system.

A diesel engine injection pump injects fuel into the firing piston chambers of diesel engines. Understand that, unlike gasoline-powered engines, spark plugs are not used to ignite the fuel. Diesel engines rely completely on the high compression pressure of the fuel in the piston chamber to result in ignition of the diesel. Therefore, diesel injection pumps are extremely significant and must be built tough to create the compression values of up to 15,000 psi necessary for the engine's operation.

Naturally aspirated engines pull in air without mechanical help (suck) to begin the combustion process.* These diesels produce less power than their turbocharged first cousins.* Turbocharging is the mechanical forcing of air into the engine permitting it to produce more power.

Turbocharged diesels refer to any diesel engine with a turbocharger. Turbo charging is the norm rather than the exception in bigger and faster motor yachts. As with any turbocharged engine, turbo diesels can offer higher power outputs, lower emissions levels, better efficiency than their naturally aspirated counterparts.

Hi power engines requires stronger (and thus heavier) internal components such as the pistons and crankshaft to withstand the continuous lumbering from the diesel engine's operating cycle. Thusly, the heavy design of a diesel engine is made to take hundreds of hours of constant use under load.* I am told by the Westerbeke representative of one engine, still in use today that has 30,000 hours on her and she is still operating fine.

Diesels can be damaged as a consequence of misapplication or abuse namely internal glazing and carbon buildup. This is often found in generators caused by failure to run the engines not under a load ideally diesel engines should run at least about 75% of their maximum rated load and RPM. Short-term periods of low load running are permissible providing the engine is taken up to full load, or close to full load on a frequent basis.

In another article, well critique the principle problem with diesel engines the quality of the fuel.
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