Experimental and Numerical Investigation of Performance and Emissions in Compression Ignition Engines with Alternative Fuels.
Abstract
The experimental investigation in this work concerns the compression-ignition (CI)
engine combustion process both in normal operation and dual-fuel operation. There is a
bulk of literature reporting thermal efficiencies, brake specific fuel consumption (BSFC)
and emissions under single and dual fueling conditions in CI engines. Most of the studies
lack the full implications of changing load (power output) and speed on these performance
indicators. The studies are either restricted to various loads/powers at one engine speed
(neglecting the effect of engine speed) or one or two load/power conditions at various speeds
(neglecting load variations). There is a scarcity of full engine maps in the open literature
(these are the full contours of thermal efficiency or BSFC plotted throughout the power
versus speed range of the engine, or the torque versus speed range of the engine). This
thesis provides performance and emissions maps for a CI engine using two different fuels
(diesel and rapeseed methyl ester used as single fuels) and two gaseous fuels (natural gas
and hydrogen) used with two different pilot fuels (diesel and rapeseed methyl ester ) under
what is termed dual fueling mode. A novel approach is used to present the performance
and emissions over the entire engines operational range. The results are presented as iso-
contours of thermal efficiency, volumetric efficiency and brake specific NOX, specific HC
and specific CO2 on a power-speed graph throughout the operating range of the engine.
Many studies conclude that the emissions, particularly NOX during dual fueling are
expected to form in the spatial region around the pilot spray. This region is expected to be
subjected to high localised temperatures as the equivalence ratio is close to stoichiometric,
thus maximising heat release from combustion. The effect of changing the pilot fuel quantity
on performance and emissions is rarely reported. This study addresses this scarcity in the
literature and investigates the effect of changing the pilot fuel quantity and type on various
combustion and emission parameters. Diesel and rapeseed methyl ester (RME) have been
used as pilot fuels for both the natural gas as well as hydrogen and three different pilot fuel settings have been employed for each of the gaseous fuels. The effect of using a different
pilot fuel quantity to achieve the same brake mean effective pressure (BMEP) for the two
gaseous fuels has been analysed and compared.
This thesis also includes a chapter on the computational modeling of the engine
esmissions. This study uses combinations of different spray and combustion models to
predict in-cylinder pressure, rate of heat release and emissions. The approach employs
two combustion models: Unsteady Flamelet Model (UFM) with PDF method and Finite
Rate Chemistry (FRC) with stiff chemistry solver implemented through In-Situ Adaptive
Tabulation (ISAT) algorithm. Two spray models used includeWAVE and Kelvin Helmohltz
Rayleigh Taylor (KHRT) spray models. The UFM coupled with KHRT spray model has
been used to predict NOX, CO and CO2 emissions. The model captures the emissions
trends well. In-cylinder contours of O2, NO and mass average temperature have also been
presented. A chemical mechanism of n-heptane with 29 species and 52 reactions has been
used.
Authors
Imran, ShahidCollections
- Theses [3711]