Exhaust gas recirculation (EGR) is a NOx emission control technique available for a large variety of diesel engines. The configuration of a system depends on the necessary EGR rate and other particular demands of the varied applications. A majority of the EGR systems include main hardware components including one or more EGR control valves; one or more EGR coolers; and piping, flanges, and gaskets. Other specialized parts may come included in specific systems, such as venturi mixer devices and EGR pumps.
The DDC Series 60 is an example of an EGR system for a heavy duty engine, applied in North America. It is a high pressure loop (HPL) system that takes a portion of its exhaust from upstream of the turbocharger. The geometric turbocharger, among other details, assures the pressure difference between the exhaust and intake manifolds stays positive to ensure an adequate EGR flow when necessary. The EGR proceeds to flow through the EGR cooler, administered with water from the engine jacket water. Leaving the cooler, the EGR flows through an EGR pipe, crossing to the other side of the engine with a venturi-type flow meter providing a feedback signal for monitoring the EGR rate. Located before the mixer housing, the EGR control valve is responsible for controlling the EGR rate. It is passed to the intake manifold where it is mixed with coolly charged air prior to being inducted into the engine.
The Detroit Diesel Corporation US EPA 2007 series 60 received numerous changes since it originated in 2002. Older versions of this engine, such as the US EPA 2002/2004, had the EGR valve located on the inlet side of the cooler. Earlier versions even used a pneumatically actuated valve, which was replaced by a hydraulically actuated valve, which was finally replaced by a electrically actuated valve. Some engines even used pressure taps upstream and downstream of the control valve to monitor the pressure across the valve for the EGR rate feedback, rather than using a venturi-type flow meter. The venturi flow meter was completely removed by 2008. The Scania Euro IV system is another example of a cooled EGR system for heavy duty engines. Through the EGR control valve and EGR cooler, pre-turbine (HPL) exhaust is sent through the components to the engine inlet system. In this example, the cooling medium is the engine jacket water. Typically EGR systems can be cooled using engine coolant, ambient air, or a low temperature liquid.