Engine Stress

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When I began my career as a captain, attitudes were pretty lax about prophylactic diesel engine maintenance. It wasn’t that we didn’t care. We devotedly changed oil, fuel filters, zincs and seawater impellers, but anything beyond was delayed until the engines showed symptoms. But back then, 20 knots was blazing speed, and a bit of diesel smoke was part of the allure of the sea. Symptoms came on gradually too. A little extra smoke or slightly elevated temperatures necessitated an injector change or heat exchanger cleaning, when convenient.

Since then horsepower has tripled within a given-size engine. Fuel economy is up while exhaust emissions are way, way down. But this stresses an engine’s components to the maximum. What could wait in years past can now ruin an engine in hours, minutes or even seconds. Preventive maintenance and careful attention to fuel are the keys to long life from today’s engines.

“The attitude used to be ‘If it isn’t broken, don’t fix it,’” says Charlie Schloemer, president of Palm Beach Power in West Palm Beach, Florida. This carried through the ’80s as the quest for improved horsepower-to-weight took hold, but back then captains joked that some engines broke down so often they should be held together with zippers, not bolts, to speed repairs.

Today, manufacturing methods and materials, computer simulations, sophisticated monitoring and decades of experience help manufacturers keep engines trouble free. They also bring a much better understanding of wear. “Manufacturers determine maintenance schedules based on thousands of hours of experience with those engines,” Schloemer says. On MTU diesels that Schloemer works on, he says, “exhaust valves need to be adjusted every 500 hours. They do wear.” Those valves are worn not by engine hours, but by how much burned fuel passes through them, exemplifying changing maintenance needs as horsepower increases.

Fuel delivery has changed the most. “It’s tighter tolerances within the fuel system that allows us to have more precise control over timing of the injection, the quantity of fuel and higher pressures that result in better fuel atomization,” says Dan Burns, an engineering manager with Cummins MerCruiser Diesel. But tight clearances won’t tolerate contamination. “A 50-micron particle might flow right through, but get a 10-micron particle in the wrong spot and you bring an injector to a stop,” Burns says.

Thirty-micron primary filters and 10-micron secondaries, common a decade ago, have been replaced by 10- and 2-micron filters — for particles smaller than red blood cells and many bacteria. Change these filters regularly, Burns says, but more important is a quick daily inspection of fuel filter bowls (image below). “We’ve built in alarms, but there is no comparison to checking yourself,” he says. Clean fuel is “clear and bright,” not hazy, and either golden or dyed red for tax reasons. Just a bit of contamination in the filter bowl is normal, but anything more is an expensive gamble, because injectors can now exceed $1,000 each.



The reverse is also true. “If properly maintained, I expect a common-rail fuel system to last the life of the engine,” Burns says. Some engines even calculate and compensate for wear of injector nozzles, extending their service life. Limitless control over fuel delivery allows multiple, tiny early and late injections to clean exhausts and mitigate internal engine stress.