By John Baxter
Some in the engine market say SCR will be a lot like turning the clock back to the happier, more fuel-efficient days of the late 1990s, before the advent of EGR. While SCR offers some advantages, its overall value versus EGR-only technology is complicated by having to account for its higher costs and its dependence upon an onboard exhaust additive, diesel exhaust fluid.
Proponents of SCR say it will be like a breath of fresh air to diesel owners in terms of dialing back EGR’s intrusive effects. When EGR entered the picture in 2002, it brought variable geometry turbochargers, increased fuel consumption and stresses on the engine oil, and a jacket water EGR cooler and EGR valve that sometimes gave trouble. In 2007, an increase in the percentage of the exhaust that was recirculated was combined with a diesel particulate filter that uses a significant amount of fuel to regenerate itself in some applications. But with SCR, less exhaust will be recirculated, so engines will behave more like they did in the past.
Turning back the clock, however, comes at a price – for the initial cost and in operation. Schneider National’s Steve Duley, vice president of purchasing, says his company’s research shows DEF is likely to cost $2 to $3 per gallon.
Duley’s heard the increased cost of engines with SCR systems will be $5,000 to $8,000. Eric Starks, president of Freight Transportation Research Associates, says his clients are hearing $5,000 to $10,000. Such estimates are similar to the hikes that accompanied the introduction of 2007 technology.
Part of that cost will be the upgrade to the onboard diagnostics – also necessary with Navistar’s system – needed to control the system and signal trouble. (For more on ODB, see “Future Focus,” page 29.) However, “There may be some integration between the various components, and that may help with the cost,” Duley says. “Also, the DPF is likely to perform better, going longer between regeneration cycles.”
For most SCR systems, the only change in maintenance will be replacing a simple filter near the dosing valve once every year or two. In Mack’s case, “The only predicted SCR system maintenance is the actual DEF injector annually and the DEF tank filter which is also on an annual PM schedule,” says David McKenna, marketing manager for Mack drivetrains.
Cooling SCR engines will not be a problem, say Stephen Morelli of Daimler Trucks North America, and Preston Feight, Kenworth’s chief engineer.
