When electronic engine management appeared on agricultural diesels a decade ago, manufacturers said farmers would see better fuel economy, better performance and less maintenance.
The driving force behind the new technology, however, was anticipated stricter emissions standards from the U.S. Environmental Protection Agency, standards that have since been adopted widely, including by Canada.
In the past decade, these technological advances have given farmers a 15 to 20 percent increase in fuel economy, along with significant gains in horsepower and torque. Electronics allowed the precise control of fuel and air entering the combustion chamber, making diesel engines cleaner and more fuel efficient.
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On the down side, farmers found that fuel must be impeccably clean or those advantages disappear.
But more recently, engine makers have been focussed on meeting government emission standards. Tier 2 emissions criteria came into effect in 2004 and will continue to phase in for the next five years until Tier 3 takes over. These regulations have placed emissions as the top priority, trumping fuel economy, performance and cost of maintenance.
“It’s the law,” said Lorne Lagimodiere of Toromont Caterpillar in Winnipeg.
“A manufacturer cannot sell a diesel engine today unless it meets Tier 2 criteria. That criteria places fuel economy and maintenance costs into a secondary position. That’s just the way it is – no argument.”
Lagimodiere said the culprit being addressed is nitrogen oxide emissions. Conventional wisdom on diesel efficiency supported high combustion chamber temperatures because they burned the fuel more completely, producing more power with fewer emissions.
The high temperatures solved some problems, but also caused production of nitrogen oxide, a major component of ground level ozone, or smog, and a greenhouse gas.
In an attempt to lower combustion chamber temperatures, some diesel engines use a system that reintroduces some of the oxygen-depleted exhaust gas back into the induction system. Because the oxygen has already been consumed, this dead air helps solve the temperature problem, but does not necessarily create a more powerful or fuel efficient engine.
Caterpillar
Lagimodiere said Caterpillar Tier 2 engines use a different approach. Rather than recycling exhaust gas through the combustion chamber, they fill it with a higher volume of fresh atmospheric air, including oxygen.
“To accomplish this, we run twin turbochargers, with very high air pressure and very high air volume,” he said.
“The next part of the design is to hold each intake valve open longer. The camshaft lobe continues its normal rotation, but an electric solenoid holds the valve open. We still have the valve open to let in more fresh air, even after the piston has gone down and starts to come up again.”
He said the increased air flow cools the cylinder on every cycle. With the high turbo pressure, exhaust gas is blown out sooner and the compression chamber fills with fresh air sooner.
“We’re not convinced that running dirty exhaust gas back through the combustion chamber is good for the pistons, rings and liners, and it puts a lot of contaminant in the oil,” he said.
“We expect our 13-to-15 litre engines to go 20,000 hours minimum. These new engines will last that long or longer and they meet the new emissions criteria.”
This technology addresses emissions but does nothing for fuel efficiency.
“I think fuel economy in diesel engines has become stagnant at this level, right across the industry,” Lagimodiere said.
“We’re not likely to see the big gains we experienced in the past decade.”
John Deere
John Deere complies with Tier 2 requirements by concentrating on precise fuel delivery, said Dave Thiessen of Enns Brothers in Morris, Man.
“On some of our latest systems, we’re running 28,000 psi on the injectors,” he said.
“I would have to think we’re close to total atomization of the fuel at that pressure. There are no liquid droplets going into the combustion chamber.”
Thiessen said fuel economy improvements since the first computer-controlled diesel John Deere engines 10 years ago have been good, probably averaging 15 percent.
“We’ve had significant feedback from our customers in the past few years. Unfortunately, I think we’ve reached the limits in fuel economy for now. The maximum injector pressure we can attain is 30,000 psi with the materials currently available. So, I don’t think we’ll see any real improvements in fuel economy in the near future.”
Deere is also developing exotic materials for pistons and other components.
“Once those are available to the production line, I think that’s when we’ll see the next round of improvements in fuel economy.”
Cummins
The Cummins QSX was designed with the coming Tier 3 criteria in mind. It employs a unique dual overhead cam system, with the first camshaft driving the 30,000 psi fuel injection system. High injection pressure means a more efficient engine.
The second camshaft has the usual lobes for the intake and exhaust valves, as well as another set of lobes dedicated to an integrated engine brake system.
The integrated electronic engine management system gives the operator several horsepower and fuel economy options. As field requirements change, the operator can switch from one torque curve program to another, thus making optimal use of every gallon of fuel.
When high quality diesel fuel is not available, the engine management system is capable of tuning itself to run at optimal efficiency on a variety of alternate fuels, including kerosene. The performance characteristics adjust continuously to compensate for changes in temperature, atmospheric pressure and humidity.
An automatic sensor alerts the operator when water-contaminated fuel is in the system.
