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​The More Fuel, The More Waste Heat Part 1. The Cooling Effects Of Charge Air And Boost

By Fernando DeMoura

January, 2019

The most common question people ask me is how much horsepower a Series 60 can tolerate. Most expect I’ll give them a one or two sentence answer, and I try to, but I could write a book on how complex the answers actually are. Maybe one day I will. For today I’m going to talk briefly about one of the many factors to consider.

Any machine with one or more moving parts produces waste heat in various forms. The more work you get out of a machine the more waste heat. There are no exceptions to this and it doesn’t matter if your machine burns fuel or runs on batteries. When energy changes from one form to another you get waste heat. A few years ago, I spoke with a Tesla engineer who told me the main problem holding back the Tesla highway tractor was the waste heat produced by the batteries. When the truck pulled a load up a long grade the waste heat generated from the discharging batteries boiled off the glycol water jacket. So, at high load these guys were forced to run cooling fans from already taxed batteries to regulate the battery coolant. Output at high load becomes inefficient. Sucks to be them.

Internal combustion engines have an inherent waste heat cooling advantage over battery powered vehicles. The more horsepower a 2 stroke, a 4 stroke, a rotory, or even a jet turbine produces more air moves through the engine. That air provides cooling that is proportional to the engines power output. 

The engine dyno I used to run a few years ago had two coolant tanks that would manage engine waste heat during a test. The first tank had a submerged radiator and the second tank had a submerged charge air cooler. Both tanks had roughly the same volume and exchange rate. Nine precision temperature probes fed the dyno computer data from both tanks as well as the turbo compressor inlet, turbo compressor outlet, intake manifold, exhaust gas, water, oil, fuel, and ambient air temperatures. The system worked well. At high engine loads the charge air cooler tank would run hotter than the radiator tank.

We know most of the waste heat generated from these engines is coming directly from combustion gas. The denser and cooler we can make the charge air the more oxygen is available to burn and the more energy the charge air can absorb before it turns into 1400-degree exhaust gas. ECM programs typically require a boost reading of 14 psi or more before allowing full fuel. If ECMs didn’t derate a major boost leak would cause exhaust gas temperature to shoot through the roof and damage the engine as surely as running out of coolant would. If you have a high-quality Hewitt boost and exhaust gas temperature gauge with a thermocouple in the manifold, you can watch the cooling effects of boost as the engine takes on load. As the engine load increases boost will come up and exhaust gas temperatures come down. 

Next month I’ll talk a little about dealing with waste heat on the other side of the piston.

Fernando DeMoura, Diesel Control Service 412-327-9400