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The More Fuel, The More Waste Heat Part 2. Keeping The Pistons Cool.

By Fernando DeMoura

February, 2019

The most common question people ask me is how much horsepower a Series 60 can tolerate. For today I’m going to talk briefly about one of the many factors that play into that question.

Last month I talked about how charge air volume and density can help cool the cylinders and lower exhaust gas temperature. This month let’s think about dealing with waste heat on the other side of the piston.

Internal combustion engines produce waste heat that’s loosely proportional to the amount of work they produce. If we want an engine to be able to maintain full load without damage, we have to control the temperature of the pistons, the rings, the skirts and the wrist pins. Most catastrophic failures I’ve seen have started here. When steel gets to about 1200 degrees Fahrenheit its strength is cut roughly in half and at full load you really don’t want that. Coolant, oil, and cooled charge air help cool the piston assembly but when you watch these temperatures keep in mind the values you see are only averages. The oil that’s returning from underside the pistons or the turbo oil drain tube is much hotter than the oil temperature that’s in the pan. During high horsepower chassis dynamometer tests, I’d usually be in the control room behind three 20-inch computer monitors. I’d watch as the dyno, emissions, and ecm data streamed in on three different computer screens. The dyno operator and I would be on a radio and if either one of us smelled burning oil I’d grab my safety goggles and check the crankcase breather. If smoke was pouring out, we killed the test. When oil supplied to the wrist pins starts to burn it won’t show up on any sensors. Coolant, oil, and exhaust gas temperature can all look normal even while piston temperature starts to rapidly climb. I saw a stock Caterpillar do this and it turned out that a piston cooling nozzle was about 20 degrees out of alignment. That was all it took to cause that cylinder to overheat.

It’s very important to know which Series 60 you have. Thanks to the versatility of DDECs and the Series 60 injection system all 12.7s can make power but some models can tolerate the fuel and the heat better than others. There are many factors to consider but right now let’s look at managing piston temperature in two Series 60 12.7 engines.

First let’s look at a 1996 GK60 running at full load and 1400 degrees exhaust gas temperature. The highest factory rating for these engines is 470hp 1550ftlbs. To produce 1400-degree exhaust gas temp after the turbo this engine would have to be turned up…a lot. An older GK60 does not have piston cooling nozzles. Compared to a BK60 a relatively low volume of oil is cooling the bottom of the piston though an oil galley in the rod. The operators of these engines need to be aware that if the engine is turned up and is being held at full load and worse yet being lugged the amount of oil cooling the piston isn’t going to keep up with the heat generated from the extra fuel for very long. Applications without much weight or long grades might be ok but otherwise the operator should not stay at full load for very long. Now let’s look at a BK60 with piston cooling nozzles. Running at 1400 degrees. 

That extra oil volume on the bottom of the piston strips away more heat. A BK60 might run a slightly higher average oil temperature but I’d rather have more heat in my oil where the oil cooler can get rid of it then in my pistons.

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Written by Fernando DeMoura

Diesel Control Service.

Phone 412-327-9400

Website: www.dieselcontrolservice.com

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