![]() ![]() The venturi is used to increase the available pressure differential between the exhaust and intake manifolds, which can be limited on efficiently turbocharged engines. The EGR valve is used to close the EGR path during start-up and during periods when the engine coolant is below a prescribed value. EGR is drawn from the exhaust manifold upstream of the turbocharger turbine and transferred to the intake manifold via a flow control orifice and a vacuum-actuated EGR valve. The Cummins TLEV automotive engine uses a form of open-loop control of EGR as shown in Figure 11.18. The EGR system is subject to on-board diagnostic requirements for emission controls as described in Section 11.3.7. EGR is controlled electronically in response to throttle demand and ambient conditions. heavy-duty transient emission cycle shown in Figure 11.1. In this application the engine is certified on the U.S. The engine was developed to meet the stringent California Transitional Low Emission Vehicle (TLEV) standards for heavy-duty engines. produces a version of its 5.9-litre B-series, DI diesel engine for the Dodge Ram light truck with uncooled EGR. In the United States, Cummins Engine Company, Inc. An increasing number of passenger-car diesel engines are using cooled EGR as a means of improving the NO x/fuel consumption trade-off at low emission levels. Since flame temperature is also a function of intake manifold charge temperature, further gains in NO x control may be achieved by cooling the EGR prior to mixing with the charge air. At higher loads the delivery of EGR is not so readily achieved while maintaining adequate air-fuel ratio hence, it is more usual to rely on alternative strategies such as retarded injection timing under those conditions. In light-duty applications, the engine is used mainly in the lower load and speed range, where high EGR rates (30 percent to 60 percent) are easily achieved. A typical EGR control map for a passenger-car diesel engine is shown in Figure 11.17. European passenger car diesel engines use EGR to meet ECE-15 Stage 2 emissions, whether IDI or DI combustion is used. The tightening of emission standards has led to increased application of EGR for automotive diesel engines.
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