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Penny-pinching power plants

Agriculture.com Staff 07/16/2009 @ 1:13pm

The rapid refinements that have marked the evolution of the diesel engine since the early 1990s have created power plants that leap at the opportunity to generate extra horses when conditions call for that response.

Farmers responding to a Machinery Talk survey on Agriculture Online recognize that today's diesels grow extra power to do tasks like till through a tough patch in the field or unload on-the-go with a combine.

Yet not a single farmer responding to that poll acknowledges that today's Tier 3 (an EPA standard set forth to reduce pollution) and newly introduced Tier 4 engines are misers when it comes to fuel.

Take John Deere's Model 8430 tractor, for example. Its Tier 3-compliant PowerTech Plus 9.0-liter diesel consumes 9% less fuel than the preceding Tier 2 engine. In doing so, the 8430 set fuel-efficiency records at the Nebraska Tractor Test, points out John Piasecki of John Deere Power Systems.

A good example of how engineers are milking more power from less fuel can be found in the use of exhaust gas recirculation (EGR). This system grabs a portion of manifold exhaust and directs it through a cooler (positioned ahead of the radiator) that reduces the air's temperature. Cooled EGR air is portioned into the intake airstream. This reduces the oxygen content and lowers the temperature of combustion air, which increases the density of the air to provide for more thorough fuel combustion.

Then, too, today's fuel-injection pressures are astronomical compared with 1990s engines. Injectors now operate at 22,000 psi and higher to fully atomize fuel in the cylinder. Injectors are also positioned vertically between dual sets of intake and exhaust valves and directly over the center of symmetrical piston bowls.

This location allows multiple streams of highly vaporized fuel to be dispersed around the cylinder so it can readily mix with incoming air. The injectors are fed by a high-pressure common rail system linked to electronic controls that precisely deliver fuel to match engine loading and throttle settings.

"Maintaining peak injection pressure is no longer dependent on engine speed, load conditions, or fueling capability," says Marco Rangel of Cummins. "Injection pressure can be virtually constant at all speeds, realizing greater flexibility and precision in controlling both injection rates and timing."

There is a cost to this technology. Today's high-horsepower diesels are 20% to 40% more expensive. But these power plants offer longer life thanks to the use of high-strength and hardened steel components.

The rapid refinements that have marked the evolution of the diesel engine since the early 1990s have created power plants that leap at the opportunity to generate extra horses when conditions call for that response.

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