Date of Award

1-1-2007

Publication Type

Doctoral Thesis

Degree Name

Ph.D.

Department

Mechanical, Automotive, and Materials Engineering

Keywords

Biodiesel, common-rail diesel engines, diesel fuel, EGR, HCCI, HTC, ignition delay, LTC, simultaneous reduction of NO x and soot, 0-D modelling

Supervisor

Ming Zheng

Supervisor

David S-K. Ting

Rights

info:eu-repo/semantics/openAccess

Abstract

The main objective of the work underlying the dissertation was in-cylinder simultaneous reduction of nitrogen oxides (NOx) and particulate matter (PM) in diesel-/biodiesel-fuelled engines. Empirical investigations were performed for comparisons between (1) engine cycle performance of conventional diesel high and low temperature combustion processes (HTC and LTC), and (2) the use of neat commercial biodiesel and conventional diesel in the HTC and LTC modes. A four-cylinder common-rail direct-injection (DI) diesel engine and a single-cylinder DI engine with mechanical injection configuration were employed. The tests were conducted under independently controlled single- and multi-event injections, exhaust gas recirculation (EGR), boost and backpressure to achieve the LTC mode. Furthermore, engine cycle, chemical kinetics and multi-dimensional simulations were performed primarily as tools facilitating the explanation of empirical results. Deduced from extensive empirical analyses, the exhaust emissions and fuel efficiency of the diesel engines employed characterised strong resilience to biodiesel fuels when the engines were operated in conventional HTC cycles. The results offered a promising perspective of the neat biodiesel fuels. As the engine cycles approached the LTC, dissimilar engine performance between the use of conventional diesel and biodiesel fuels was observed. In the late single-shot strategy with heavy EGR rates (EGR-incurred LTC), which could be utilised to improve the fuel efficiency of diesel/biodiesel LTC cycles at low loads, the biodiesel was found to sustain a broader range of loads than the diesel fuel. This was mainly attributable to the biodiesel's higher Cetane number (CN) and combustion-accessible fuel oxygen. At high load LTC, the diesel fuel early-multiple injections with EGR facilitated mixture homogeneity that is more difficult to generate with a single pulse injection. Conversely, the biodiesel early-injection strategy presented numerous challenges apropos of the homogeneous fuel/air mixture formation, especially at medium-to-high load conditions. This was attributed to the low volatility and high viscosity and CN of the investigated biodiesel fuel. The empirical analyses, especially involving the EGR-incurred LTC, presented a platform for model-based control with an improved ignition delay correlation. The new correlation, which considered the CN and oxygen concentrations in the fuel and intake air, captured the ignition delay trends with good agreement.

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