Cummins demonstrates EGR

While caterpillar “acerts it won’t need EGR” (see CCJ, Maintenance & More, May 2001), Cummins Inc., Columbus, Ind., is convinced that engine jacket-water-cooled EGR (exhaust-gas recirculation) is the best way to meet the reduced heavy-truck-engine nitrogen oxides (NOx) standards for 2002.

Cummins has been “on this path for over a decade,” says John Wall, Cummins’ vice president and chief technical officer. He cites research that suggests to Cummins that cooled EGR has the least effect on fuel economy while reducing NOx. According to Cummins’ simulations, “Even with an infinitely flexible fuel system – that is, optimized injection rate shaping, which is better than retarded timing alone – NOx still won’t be down where you want it to be,” Wall says. The problem, Cummins says, is that combustion would still occur a bit too late in the power stroke, reducing fuel economy. With EGR, however, combustion can occur right on time.
Wall and his associates, including Rich Kleine, director of automotive customer engineering, in charge of packaging Cummins’ EGR system, stress what Cummins sees as “a new paradigm.” They believe that increasing engine heat rejection – instead of trying to hold the line on heat rejection – equates to a noticeable improvement in fuel economy. More efficient radiators and more powerful fans can shed more heat with no change in hoodline, while improvements in water pump efficiency can minimize parasitic losses.

At a recent news briefing at its headquarters, Cummins demonstrated a system that fits easily into a typical engine compartment and performs well on the road. To keep particulate emissions from going up, the cylinder must contain just as much oxygen as it does without EGR. That means that with 20 percent EGR, the cylinder pressure must rise. But the Signature/ISX engine was designed for 2,800-psi peak pressures, so engine life should not be affected, Cummins says.

The resulting system has titanium turbine blades and a water-cooled turbo housing. Intake manifold pressure normally is higher than exhaust back-pressure. But the engineers want the exhaust to enter the intake system after the turbo and aftercooler to prevent overcooling and condensation of water and acids. So, this turbo is equipped with a variable geometry nozzle, allowing increased throttling of the exhaust right before it enters the turbine. This raises back pressure until it slightly exceeds intake pressure so the exhaust will flow into the intake manifold.

The gas first enters an EGR valve mounted on the exhaust manifold. It then passes through the stainless steel cooler (mounted on the right side of the engine), loops around the rear of the engine and flows forward into a venturi-mixer. Here, flow is measured via restriction – the resulting pressure drop is measured with two sensors and sent to the engine ECM.
The system then regulates flow by varying the opening size of the turbine nozzle, as well as the opening of the EGR valve, much as you might regulate both hot and cold water valves in a shower. Turbine rpm is also sensed and input to the ECM. The system constantly adjusts the size of the turbine nozzle according to operating conditions. Drivers often comment that the turbo speeds up when least expected to. The EGR valve not only helps govern flow, but also closes entirely to keep exhaust from entering the cooler and condensing during early stages of warm-up.