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A significant driver for the development of future commercial vehicles is likely to be the introduction of fuel consumption related legislation in various regions around the world. The application of a waste heat recovery system to the powertrain of such vehicles is seen as a possible step, amongst many, to help them achieve the required fuel economy. In particular, the Rankine Cycle (a closed steam cycle) is often proposed as a potential means for deriving work from the engine exhaust heat. Rankine Cycle systems are already in use in off-highway applications, such as stationary engines or marine power-packs. However, the technical and commercial viability of these systems for on-highway, principally long haul truck application is as yet unproven. Aspects such as the in-use economy benefits, the system performance density, the component robustness and all interactions with the other vehicle systems have to be evaluated.

In relation to further tightening of the emissions legislation for on-road heavy duty Diesel engines, the future potential of cooled exhaust gas recirculation (EGR) as a result of developments in the cooling systems of such engines has been evaluated. Four basic engine concepts were investigated: an engine with SCR exhaust gas aftertreatment for control of the nitrogen oxides (NOx), an engine with cooled EGR and particulate (PM) filtration, an engine with low pressure EGR and PM filtration and an engine with two stage low temperature cooled EGR also with a particulate filter. A 10.5 litre engine was calibrated and tested under conditions representative for each concept, such that 1.7 g/kWh (1.3 g/bhp-hr) NOx could be achieved over the ESC and ETC. This corresponds to emissions 15% below the Euro 5 legislation level.

Step by step US and European legislation are defining more stringent emission limits for diesel engines. Depending on these limits for NOx and particulate emissions different emission reduction concepts including or excluding cooled exhaust gas recirculation (EGR) appear over time. Most probable cooled EGR will be the solution for US02 and, in combination with particulate traps, for many Euro4 applications. Competitive aftertreatment solutions like selective catalytic reduction (SCR) may need cooled EGR in addition to meet even tougher emission targets. Therefore cooled EGR can be assumed to be a long term task. The impacts on the power train cooling system arise from the need of high performance EGR systems. This results in increased heat rejection from the EGR cooler and increased pressure and temperature loads on the charge air cooling system.