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Combustion process in a Two-Stroke, H2-DI Linear Generator Free-Piston Engine during starting

Hanipah, Mohd Razali Bin Hanipah (2008) Combustion process in a Two-Stroke, H2-DI Linear Generator Free-Piston Engine during starting. Masters thesis, UNIVERSITI TEKNOLOGI PETRONAS.

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Abstract

A two-stroke free piston engine (FPE) for the application of a linear generator (LG) has been developed. It is a direct injection, spark ignition engine fuelled by hydrogen. In the past, the starting strategy of the FPE was based on the crank slider engine. However, the requirement of a different strategy is inevitable since the LG-FPE has no flywheel and has variable compression ratio during motoring. In addition, without a flywheel the engine has no energy storage to maintain its inertia in case of a misfire during starting. The fuelling amount, fuel injection and ignition timing during starting of LG-FPE is different from a conventional crank-slider engine. Starting of the former is done by accelerating a total moving mass of 5kg alternately via electrical commutation of the linear motor towards both ends of the cylinders’ stroke until sustainable combustions are achieved. The main objective of this research is to empirically investigate and determine the optimum injection and ignition timing during motoring with combustion when starting the LG FPE. Intake airflow measurements were obtained using laminar flow element setup. This is to determine the initial setting for hydrogen fuelling at stoichiometric air-fuel ratio. The investigation was carried out by varying the start of fuel injection (SOF) at constant start of ignition (SOI) and fuel per cycle (FPC) during motoring with combustion experiments of LG-FPE. Next, the SOF and FPC are kept constant while varying the SOI. Finally, the FPC was varied at constant SOF and SOI values. Combustion process analyses were done by focusing on the rate of heat release, mass fraction burned, and ignition lag and combustion duration. From these analyses the optimum settings for SOF were found to be at linear position of+25.0 mm for cylinder 1 and -25.0 mm for cylinder 2. Early SOF setting resulted in lower peak pressure and slower rate of heat release while the ignition lag and combustion duration is longer. Whereas, the optimum settings for the SOI were found to be at position +29.5 mm for cylinder 1 and -30.0 mm for cylinder 2. The SOI must be before the peak pressure of compression (i.e. before the piston reverses direction). The timing must provide sufficient time for the flame to develop so that the piston will be in opposing motion in time for the heat release rate and cylinder pressure to reach its maximum. By using hydrogen instead of CNG, the ignition lag is reduced by 66% while the combustion duration is 50% faster.

Item Type: Thesis (Masters)
Subject: UNSPECIFIED
Divisions: Engineering > Mechanical
Depositing User: Users 5 not found.
Date Deposited: 05 Jun 2012 08:37
Last Modified: 25 Jan 2017 09:44
URI: http://utpedia.utp.edu.my/id/eprint/2936

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