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

Hanipah, Mohd Razali (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 Skg 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 (SOl) and fuel per cycle (FPC) during
motoring with combustion experiments of LG-FPE. Next, the SOF and FPC are kept
constant while varying the SOL Finally, the FPC was varied at constant SOF and SOl
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 SOl were found to be at position +29.5 mm for
cylinder I and -30.0 mm for cylinder 2. The SOl 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)
Subjects: T Technology > TJ Mechanical engineering and machinery
Departments / MOR / COE: Engineering > Mechanical
Depositing User: Users 2053 not found.
Date Deposited: 09 Oct 2013 11:07
Last Modified: 15 May 2023 03:56
URI: http://utpedia.utp.edu.my/id/eprint/8281

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