Exhaust gas recirculation lowers pollutant levels and fuel consumption

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Stuttgart, Germany, September 2010—Better fuel economy and lower pollution emissions are top priority on the development agenda. With application-specific exhaust gas recirculation, MAHLE effectively lowers emissions and fuel consumption in engines.

In addition to reduced consumption, another important task is the prevention of pollution emissions, specifically nitrogen oxide emissions. Three promising approaches are as follows:

  • Engine without EGR, exhaust gas aftertreatment with oxidation catalytic converter (DOC), particulate filter (DPF), and SCR (NOx conversion rate >> 90%)
  • Engine with single-stage cooled EGR system (20–30% EGR rate), exhaust gas aftertreatment with DOC, DPF, and SCR (70–85% conversion rate)
  • Engine with dual-stage cooled high-EGR concept (EGR rate > 40%), exhaust gas aftertreatment with DOC and DPF

In high-EGR concepts, the required NOx limits can be achieved without cost-intensive nitrogen oxide exhaust gas aftertreatment. This configuration requires high-capacity, usually dual-stage, cooling of the recirculated exhaust gas and a high-performance particulate filter. Even so, this concept is the most cost-effective comparatively, and is the easiest to integrate into any vehicle or engine combination.

However, the volume of the EGR air mass is limited by the pressure gradient between the exhaust gas line and charge air line—a pressure gradient that is not always sufficient for high EGR rates, particularly at low engine loads and speeds. To achieve the required EGR rates of over 40%, the charge air mass flow must be throttled; this increases fuel consumption due to higher charge exchange losses.

MAHLE has therefore developed a fast-switching charge air valve (SLV), which replaces the conventional throttle valve. A brushless DC drive allows the flap to rotate continuously in synchronism with the engine speed. This not only ensures higher EGR rates of up to 50%; it also lowers the entire maximum pressure and temperature levels, thereby lowering NOx emissions as well. In addition, by decreasing gas exchange losses by nearly 50%, the SLV provides significant consumption advantages compared to a conventional high-EGR solution with a throttle valve. SLV technology has already been tested successfully in a number of commercial vehicle and passenger car diesel engines with different turbocharging concepts.

The MAHLE Group is one of the 30 largest companies in the automotive supply industry worldwide. With its two business units Engine Systems and Components and Filtration and Engine Peripherals, MAHLE ranks among the top three systems suppliers worldwide for piston systems, cylinder components, as well as valve train, air management, and liquid management systems. The newly formed Industry business unit bundles the MAHLE Group's industrial activities. These include the areas of large engines, industrial filtration, as well as cooling and air-conditioning systems.

In 2009, the MAHLE Group generated sales of approximately EUR 3.9 billion; around 43,000 employees work at over 100 production plants and eight research and development centers.