The basic premise of a conventional turbocharger is that exhaust gas still contains energy that can be put to work.
The rerouted exhaust spins the turbo, which pumps more air into the combustion chamber, where it creates more power. It works on diesel and gas engines.
But now, engineers at Case and New Holland have taken the concept further by extracting even more energy from the exhaust gas that comes out of the conventional primary turbocharger. This exhaust spins a secondary turbocharger, which then feeds rotating power down to the engine’s crankshaft.
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The process is called compound turbocharging and dates back more than six decades.
“The technology was used in World War Two in a couple of European aircraft,” said Sean Dorosz with New Holland in Pennsylvania.
“It wasn’t necessary to use it again until recently when the agricultural industry became concerned with fuel economy. This is one way of getting more work out of the same litre of diesel.”
The compound turbo engines fitted into Case and New Holland implements are Iveco diesels manufactured in conjunction with CNH.
Dorosz said the compound turbo gives these engines better fuel economy and better power compared to a conventional single turbocharger.
New Holland engineers tested the compound turbo in a side-by-side field test. They used a tractor with a conventional 15 litre single turbo engine and an identical tractor with a 13 litre compound turbo engine.
“Both units pulled identical implements side by side for 800 hours in actual field conditions. After 800 hours, the 13 litre compound turbo engine used three percent less fuel versus the 15 litre engine while accomplishing the same work.”
Dorosz said a compound turbo is not the same as a twin turbo charger system.
“Exhaust gases are routed into a secondary turbine instead of exiting to the atmosphere through the exhaust pipe. These gases spin the power turbine,” he said.
“This secondary turbine is connected to the engine crankshaft via a set of gears and a hydro coupler called a Voith Coupler. It acts the same way as a torque converter in your car’s automatic transmission. There’s no direct mechanical linkage between this new power turbine and the crankshaft because the Voith Coupler is oil filled.
“In the diagram, the left half of the Voith Coupler is spun by the exhaust gases exiting the primary turbo on the engine. This spinning moves or throws oil over to the right side of the coupler. The right side is given energy and starts spinning by the action of the moving oil. This right side is connected down to the engine’s crankshaft.”
He says that at idle, the oil in this coupler is not really moving or transferring energy.
However, when the tractor is working, the oil is passing energy across the gap and giving more energy back to the crankshaft to help the engine do the required work.
“We’re getting more work out of the same amount of fuel. By using the exhaust gas twice, we gather more energy versus letting the energy escape into the atmosphere.”
