Diesel Issue Resolution Team Action Table
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Engine performance at high altitudes-
Controlling the fuel-to-air ratio of a diesel engine is a means to limit the gaseous and diesel particulate matter emissions of the engine. At high altitudes the air density and pressure is lower. With less air available the fuel injection rate must be reduced to keep the same fuel-to-air ratio. This reduction in fuel is referred to as "fuel deration." Newer, electronically controlled engines may change the engine's timing rather than change the fuel injection rate to reduce emissions at high elevations. MSHA is evaluating the effectiveness of this method of reducing emissions. MSHA has also determined that some engines equipped with turbochargers that force more air into the engine instead of reducing the fuel injection rate may still require deration. Since the turbocharger may only provide increased air to the engine at high power output, emissions can increase above their sea level values at low power levels. This is especially true of high horsepower pickup trucks that normally operate at low power levels. Even at high power output, there may be a need to derate these engines to maintain the fuel-to-air ratio.

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