Date of Award

2009

Publication Type

Doctoral Thesis

Degree Name

Ph.D.

Department

Mechanical, Automotive, and Materials Engineering

Keywords

Applied sciences, Combustion, Diesel fuel, Nitrogen oxides, EGR, In-cylinder diagnostics, Adaptive control, Systematic control

Supervisor

Dr. Ming Zheng

Rights

info:eu-repo/semantics/openAccess

Abstract

The conventional high temperature diesel combustion is constrained by the classical NOx-soot trade-off, so that any technique to reduce one emission generally increases the other. The simultaneous low NOx and soot can be achieved by lowering the combustion temperature and by preparing a cylinder charge of high homogeneity. However, the lowered combustion temperature may significantly reduce the fuel efficiency of such combustion cycles. Therefore, the overall objective of this work was to conduct a detailed analysis of the diesel LTC cycles that result in simultaneous low NOx and low soot, and to improve the LTC performance through advanced diagnostics and combustion control strategies. The empirical and analytical analyses in this dissertation provide an in-depth understanding of diesel LTC and present an effective strategy for navigating the narrow LTC corridors.

The in-cylinder gas sampling tests culminated with the identification of an LTC NOx mechanism whereby the NOx reduction in the presence of combustibles was quantified on a crank angle-resolved basis. The intake gas treatment through catalytic oxidation and fuel reforming of EGR stabilized the LTC cycles. Novel flow management strategies were applied to improve the thermal response and the energy efficiency of the reforming operation.

Adaptive combustion control techniques were developed to improve the fuel efficiency of the LTC cycles and to enable navigation within the narrow LTC corridors. A computationally efficient `Pressure Departure Ratio' algorithm for estimating the combustion phasing in real-time was proposed along with a methodology for engine load management within-the-same-cycle, and were shown to improve the LTC operational stability. The detailed EGR analysis helped to develop a systematic LTC control strategy by quantifying the effects of intake charge dilution and boost pressure on the LTC performance metrics.

Based on the empirical and analytical analyses, the load management and efficiency improvements of the LTC cycles were demonstrated with three different fuelling strategies as follows: (1) Single-injection LTC with heavy EGR at low loads, (2) Multi-shot LTC (early HCCI) with moderate EGR for mid-load operation, and (3) Split burning LTC for higher engine loads with DPF-tolerant soot.

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