Integration of Heavy Duty Diesel Engine Technology to Achieve US EPA 2010 Emissions Compliance with Improved Efficiency

摘要

The US EPA 2010 emissions standard poses a significant challenge for developing clean diesel powertrains that are affordable. Along with exhaust emissions, an emphasis on heavy duty vehicle fuel efficiency is being driven by increased energy costs as well as the potential regulation of greenhouse gases. An important element of the success of meeting emissions while significantly improving efficiency is leveraging Cummins component technologies such as fuel injection equipment, aftertreatment, turbomachinery, electronic controls, and combustion systems. Innovation in component technology coupled with system integration is enabling Cummins to move forward with the development of high efficiency clean diesel products with a long term goal of reaching a 57% peak brake thermal efficiency for the engine plus aftertreatment system.rnThe Cummins global product strategy for diesel powertrain systems is to create engine architectures that allows system calibration to achieve a wide range of system out NOx compliance to meet the diversity of future worldwide exhaust emissions standards. A variety of engine architectures is being explored by Cummins to meet US EPA 2010 NOx emissions based on two primary strategies to control NOx: cooled EGR and selective catalytic reduction (SCR). An in-cylinder solution for NOx control based on cooled EGR can be achieved with advancements in component technology thus eliminating the need for NOx aftertreatment. The current in-cylinder architecture can achieve compliance with the 2010 NOx regulation along with particulate matter compliance with the use of a diesel particulate filter. The fuel economy of the system is comparable to that of the 2007 current product.rnMuch of the enabling technology for in-cylinder NOx control can also be used to provide significant fuel economy improvements for the variety of SCR related architectures. However, there still remains a significant fuel economy benefit associated with the SCR architectures compared to the in-cylinder NOx control architecture using the same component technology. Additional engine performance capability can be achieved in the form of increased power density for an SCR engine architecture assuming the vehicle application can accommodate a larger catalyst size. The larger catalyst poses challenges for vehicle packaging, thermal management of the catalyst bed temperature, and cost. Therefore, there exists a complex system integration and optimization task to select the right SCR catalyst size for a given power density that can involve the choice of engine displacement for a given application. Analysis and engine testing at Cummins indicate that the SCR engine architecture is better suited for engine downsizing compared to an in-cylinder solution. The power density of the in-cylinder NOx control architecture is limited by peak cylinder pressure (PCP) duernto the high rate of charge flow. If the PCP capability of the engine is increased, higher power density levels can be achieved.rnFor the engine architectures that contain cooled EGR, there exists an opportunity to recovery some of the waste heat from the EGR system and the exhaust stream. Analysis indicates that a 10% fuel economy improvement is possible with an organic Rankine cycle waste heat recovery (WHR) system. The fuel efficiency improvement can be obtained via 6% from EGR derived WHR, 2% from exhaust derived WHR, and 2% from the use of electrical accessories. Engine experiments have shown that a 5% improvement is possible from the EGR derived WHR system which is in good agreement with the analysis. Additional engine testing is planned to validate the benefits of exhaust derived WHR and electrical accessories.