Low Temperature Gasoline Combustion With Diesel Micro-Pilot Injection in a Six-Cylinder Heavy Duty Engine

Abstract

This paper describes the operation of a heavy duty six-cylinder engine in a dual fuel, Low Temperature Combustion (LTC) mode with very low engine-out NOx und soot emissions according to the US EPA Tier IV final emission limits in the corresponding C1 test cycle. This operation mode makes use of a short pilot injection of diesel fuel, which is injected directly into the cylinder, to ignite a highly diluted, premixed gasoline air mixture. Multicylinder engine operation could be demonstrated over the entire engine operating map with loads of up to 2 MPa BMEP. Expensive aftertreatment systems for NOx and soot emissions are not required. This paper also discusses the challenges involved with the implementation of this combustion system on a multicylinder engine. When transferring the dual fuel LTC from a single cylinder research engine to a multicylinder engine, the design of some engine components, e.g. the camshaft and the piston, were changed. The intake manifold is modified with port fuel injectors for ideal gasoline mixture preparation and equal distribution to all cylinders. To avoid cylinder imbalances, it is possible to control the injected masses of gasoline and diesel fuel for the pilot injection on a per-cylinder basis. Achieving high dilution for ignition delay via EGR and boosted intake pressure to avoid high pressure rise rates and knocking presents challenges for the two-stage turbocharger design. Additionally, high EGR rates and EGR cooling for increased loads are addressed. Finally, experiments to determine the significant control parameters for the combustion process are performed on the engine. In the course of these investigations, dual fuel LTC could be transferred from a single cylinder research engine to a multicylinder engine; previously obtained single-cylinder operating conditions could be achieved even at high loads.

Modeling and control of fuel distribution in a dual-fuel internal combustion engine leveraging late intake valve closings

“…These variations are indicative of uneven distribution of fuel across the cylinders and will be further addressed in this study. A prior study on a dual-fuel multi-cylinder engine by Bach et al 27 also identified uneven distribution of the port-injected fuel and significant cylinder imbalances due to the common inlet plenum and the pressure pulsations, especially during valve overlap. To obtain an even fuel distribution and a good mixture preparation, the authors of this prior study developed a new prototype intake manifold.…”

Individual cylinder fuel blend estimation in a dual-fuel engine using an in-cylinder pressure based observer

“…The aforementioned works were developed for single fuel applications, however, when dealing with dual-fuel engines, DI injection dispersion is added to PFI variability (Bach et al, 2012;Kassa et al, 2017). As previously mentioned, the portion of LRF injected plays an important role in the combustion control and pollutant formation, a proper estimation of such variable is therefore essential.…”