Experimental and numerical investigation of a high boost and high injection pressure Diesel engine concept for heavy duty applications

The upcoming European Stage V emissions regulation for Non-Road Heavy Duty Diesel Engines will force OEMs to adopt Diesel Particulate Filters, adding a further degree of complexity to the aftertreatment system, which in several cases already includes specific devices for NOx reduction. Since complex aftertreatment systems can rise packaging problems as well as reliability issues, a project in collaboration with Kohler, Politecnico di Torino, Ricardo and Denso, has been carried out to explore the feasibility of a Stage V compliant SCR-free architecture for a 90kW Non Road Diesel engine. To this scope a prototype engine based on the Kohler KDI3404, was equipped with a low-pressure Exhaust Gas Recirculation system, a two-stage turbocharger and a 3000 bar injection pressure-capable Fuel Injection System. This thesis focuses on the experimental and numerical assessment of emissions and performances of this engine architecture over the Stage V certification procedure. It will be shown how the high-pressure Fuel Injection System is the key technology to meet the stringent requirements, demonstrating how increasing the injection pressure from 2000 to 3000 bar can dramatically improve the NOx-Soot and NOx-Particulate Number trade-off, together with engine efficiency, without adversely affecting the emission of nanoparticles. Moreover, the use of extremely high injection pressures in conjunction with after injection as a soot reduction technique, was found to be capable of achieving up to 50% smoke reduction with a more than acceptable engine efficiency degradation. Thanks to a dedicated steady state and transient calibration, the engine was able to run a compliant NRSC and NRTC with more than 10% margin on NOx and a level of particulate matter and particulate number which can be easily managed by the DOC+DPF aftertreatment system. However, some components of the tested engine, such as the turbochargers, were found to be far from the optimal, thus resulting into relatively poor efficiency figures. Therefore, a 1D-CFD model featuring predictive combustion and emissions models was developed in order to assess the full potentials of this architecture on a kind of “virtual test rig”, on which different components could be easily evaluated. The model results proved that, with a better design of the exhaust and EGR line, and with a slightly higher performance turbocharger, consistent engine efficiency improvements could be obtained, making the SCR-free solution as a valuable alternative to the SCR architecture to meet the Stage V emissions regulations.