Developing a 55+ BTE Commercial Heavy-Duty Opposed-Piston Engine Without a Waste Heat Recovery System

Heavy-duty vehicles, currently the second largest source of fuel consumption and carbon emissions are projected to be fastest growing mode in transportation sector in future. There is a clear need to increase fuel efficiency and lower emissions for these engines. The Achates Power Opposed-Piston Engine has the potential to address this growing need. In this paper, results are presented for a 9.8L three-cylinder OP Engine that shows the potential of achieving 55% brake thermal efficiency (BTE), while simultaneously satisfying emission targets for tail pipe emissions. The Achates Power OP Engines are inherently 20% more cost effective. The OP Engine architecture can meet this performance without the use of waste heat recovery systems or turbo-compounding and hence is the most cost effective technology to deliver this level of fuel efficiency.The Achates Power OP Engine employs currently available engine components, such as supercharger, turbocharger and after-treatment and features a uniquely designed piston bowl shape to enhance mixing with a swirl-to-tumble conversion as the piston bowls approach minimum volume. This design improves fuel-air mixing and hence, results in low soot values, higher indicated thermal efficiency (ITE) due to better combustion phasing because of faster mixing controlled combustion and lower NO_x due to lower fueling requirement because of two-stroke and more efficient combustion system. The OP Engine has a lower heat transfer loss due to the inherent design of the combustion chamber, which provides lower surface area-to-volume ratio compared to a conventional engine. This results in further benefits of reduction in fuel consumption and green house gases (GHGs).The Achates Power OP Engine also makes use of internal exhaust gas recirculation (EGR) by using an optimized design of intake and exhaust ports that improves scavenging. This reduces engine-out NO_x along with lower requirement of flowing external EGR and hence reduction in pumping requirement. 1-D and 3-D-CFD models developed for the analysis were correlated to the Achates Power 4.9L OP Engine dynamometer measured data. The correlated models were used as tools to make predictions for the 9.8L heavy-duty engine. The optimized system include high trapped compression ratio piston bowl, ports design to provide best scavenging performance, thermal barrier coating on piston bowls and dual injector with having an optimized spray pattern layout. Results show that the OP Engine results in a BTE of 55%, while meeting stringent emission standards without the use of expensive waste heat recovery systems and/or turbo-compounding components. The Achates Power OP Engine offers a solution to the automotive industry in providing a commercially viable, highly efficient and clean heavy-duty diesel engine that will reduce GHGs and carbon footprint for heavy-duty vehicles such as Class 8 trucks.