Date of Award

2014

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Mechanical, Automotive, and Materials Engineering

First Advisor

Zheng, M

Keywords

Applied sciences, Active combustion control, Alternative fuels, Clean combustion, Diesel emissions, Engine efficiency, Low temperature combustion

Rights

CC BY-NC-ND 4.0

Abstract

The main objective of this dissertation is to improve the efficiency and emissions of compression ignition engines. Adaptive fuelling control strategies are applied for enabling the low temperature combustion on the research engines of high compression ratios using a selected set of fuels that are vastly different from the conventional diesel. These fuels include n-butanol, gasoline, ethanol, and nine diesel fuels with specifically formulated Cetane numbers, aromatic contents, and boiling temperatures. The effects of these fuels on the engine performance are compared with those of diesel in both the high temperature combustion and low temperature combustion modes in terms of the combustion characteristics, exhaust emissions, and combustion controllability. Extensive engine experiments are conducted to demonstrate that the variations in the Cetane numbers, aromatic contents, and boiling temperatures of diesel fuels, within the investigated range, have nearly negligible effects on the conventional diesel high temperature combustion. However, as the engine operation approaches low temperature combustion where the prolonged ignition delay allows the cylinder charge to undergo extended durations for physical changes and chemical reactions (pre-reactions) prior to the start of main combustion events, the changes of fuel properties start to substantially impact the pre-reactions, the subsequent combustion processes, and exhaust emissions. With the same engine hardware, the replacement of diesel with a less reactive and more volatile fuel ( e.g. n-butanol in this dissertation) significantly facilitates the enabling of low temperature combustion. The fast evaporation of n-butanol coupled with a prolonged ignition delay substantially enhances the cylinder charge homogeneity, thereby offering ultra-low nitrogen oxides and smoke emissions simultaneously. The dual-fuel combustion using a port injected fuel (gasoline or ethanol) along with a diesel pilot demonstrates desirable combustion controllability to avoid misfire or rough combustion incidences. A new combustion control algorithm correlating smoke emissions with the temporal overlap of the diesel injection and combustion events is proposed and validated with optimized engine efficiency and emissions. Ultra-low nitrogen oxides and smoke emissions are achieved simultaneously at the engine full load with ethanol and diesel fuels, which is currently unachievable with the same engine hardware for diesel low temperature combustion. Keywords : Clean combustion, low temperature combustion, active combustion control, diesel, n-butanol, gasoline, ethanol, dual-fuel, exhaust gas recirculation, near-zero NOx and smoke, emissions, engine efficiency.

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