Dimitriou, Pavlos (2015) Air-fuel homogeneity effects on direct injection diesel engine performance emission. Doctoral thesis (PhD), University of Sussex.

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Abstract

The temporal and spatial distribution of fuel in cylinders is a key factor affecting
the combustion characteristics and emission generation of a DI diesel engine. The airfuel
mixing quality is critical for controlling ignition timing and combustion duration.
Avoiding fuel-rich areas within the cylinder can significantly reduce soot formation as
well as high local temperatures resulting in low NOx formation. The present investigation
is focused on the effects of advanced fuel injections and air path strategies as well as
the effects of piston geometry and fuel spray angle on air-fuel homogeneity, combustion
process and their impacts on the performance and emission of the engine.
A Ricardo Hydra single-cylinder engine in combination with AVL Fire CFD software
was used in this investigation. An experimental analysis was conducted to assess the
combustion characteristics and emissions formation of the engine under various injection
strategies such as different injection timing, quantity, ratio, dwell angles between
injections with various exhaust valve opening times and exhaust back pressures. A quan-
titative factor named Homogeneity Factor (HF) was employed in the CFD code in order
to quantify the air-fuel mixing and understand how the air-fuel homogeneity within the
cylinder can influence the combustion and emissions of the engine.
The investigation concludes that multiple injection strategies have the potential to
reduce diesel emissions while maintaining meaningful fuel economy. Split injection can be
used to improve the air-fuel mixture locally and control temperature generation during
the start of combustion. Increased air-fuel homogeneity results in fewer fuel-rich areas
within the cylinder and contributes to the reduction of soot emission. Extending the
pre-mixed combustion phase has a direct effect on the reduction of soot formation while
NOx generation is highly dependent on the scale of the primary fuel injection event.

Item Type:	Thesis (Doctoral)
Schools and Departments:	School of Engineering and Informatics > Engineering and Design
Subjects:	T Technology > TJ Mechanical engineering and machinery > TJ0751 Miscellaneous motors and engines Including gas, gasoline, diesel engines
Depositing User:	Library Cataloguing
Date Deposited:	07 Jun 2015 11:16
Last Modified:	28 Sep 2015 14:51
URI:	http://srodev.sussex.ac.uk/id/eprint/54280

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