(273g) Mapping the Stable Region of Operation of Homogenously Charged Compression Ignition (HCCI) Engine for Methane and DMF Fuel Blend

Abstract:

The emission legislations are transmuting to be
rigid in accordance to reduce the emissions from the IC engines. Research has
been focused to ameliorate both Spark Ignition and Compression Ignition engine
in order to make them more efficient. Over the previous decade, major research
has been focused on Homogenous Charge Compression Ignition (HCCI) engines.  This engine has the potential to consummate
the eminent feature of Spark Ignition engine, with no emission of NOx and Soot
leading to cleaner combustion, the best of CI engine with higher efficiency and
low fuel combustion along with lower carbon dioxide emissions¹.

The focus of this work is to map the stable regions
of operation of HCCI engine using Methane and Dimethyl Furan blend as fuel. DMF
is comparable to gasoline since it has an energy density of 40% higher than
ethanol. Also, Burning DMF requires 33% less air compared to the same amount of
gasoline since its stoichiometric air to fuel ratio is 10.72. The Simulations
of HCCI engine were carried out in CHEMKIN, where the model used was a closed
transient CSTR². The main objective of the study was to depict the
stable regions of operation of HCCI engine with and without Exhaust gas
recirculation. EGR refers to a part of the exhaust stream recycled back to the
engine inlet along with the fuel mixture³.

Parameters such as EGR Temperature, EGR percentage
and equivalence ratio were varied to study the effect on the sustainable
emissions at the exhaust for CO, CO₂ and NOx. Detailed Kinetics of
DMF obtained from NCBI was used. Initial understanding of the working of HCCI
engine was done using Methane as source fuel, keeping EGR temperature and HCCI
engine temperatures as a constant at 600K and 447K and the equivalence ratio
were varied from 0.5 to 0.7 and the EGR percentage were varied from 0 to 30%.
The in-cylinder temperature, pressure and species profile were obtained as a
function of Crank Displacement angle (CAD).

The Figure (1) shows the effect of equivalence ratio
on the in-cylinder temperature, pressure and species profile for a engine temperature of 447K and EGR temperature of 600K for
30% EGR. Increase in equivalence ratio states the presence of higher amount of
fuel where as smaller ratios represent deficit of fuel in the mixture.  It could be observed that Peak temperature
and pressure increases with increase in equivalence ratio. The mole fraction of
CO increase with increase in equivalence ratio, this is because of the lack of
oxygen available for complete combustion. In case of Thermal NO production
rate, it increases with increase in equivalence ratio due to increase in
temperature which leads to increased production of NO at higher
temperatures.  It was observed from the
initial study using Methane as a fuel that, for Lesser
exhaust emissions, the fuel must be lean with a higher percentage of EGR.

Fig 1: Variation
of In-cylinder temperature, pressure, mole fraction of CO, CO₂ and
Thermal NO production rate with Equivalence ratio

The study was further extended to DMF as an additive
to Methane and the parameters such as EGR percentage, Equivalence ratio and EGR
temperature were varied to find the stable region of operation of HCCI engine
for Methane and DMF blend. The effect of Equivalence ratio on the in-cylinder
temperature, pressure and species properties for 0% EGR for an engine
temperature of 447K and EGR temperature of 600K were studied initially. The
figure (2) shows the effect of Equivalence ratio on Peak CO₂ mole
fraction in the cylinder for different percentage of Methane and DMF blend. It
could be observed that the peak mole fraction of CO₂ increases with
increase in Equivalence ratio and also increases with increase in blend
percentage. The latter is due to the increase in the carbon availability in the
cylinder with increase in fuel.

Fig 2: The
Variation of Peak Mole Fraction of CO₂ with percentage of the DMF
blend for different Equivalence ratios

As a next step, it is intended to study the effect
of EGR percentage and EGR mixing temperature on Methane and DMF blend as shown
in the Table 1 and analyse the Peak in-cylinder temperature, pressure and
species properties for the different parameters combinations and map the stable
region of operation of HCCI engine for Methane and DMF fuel blend.

Table 1:
Parameters to be estimated for the Blend

Keywords:

Exhaust
Gas Recirculation, DMF, Crank Rotation angle.

References:

1.     
Harrison R. M. ed. (1996) Pollution, Causes, Effects and Control. 3^rd Ed. Cambridge, The Royal Society of Chemistry.

2.     
Xu H., Liu, M., Gharahbaghi,
S., Richardson, R., Wyszynski, M., Megaritis, T.,
“Modelling of HCCI Engines: Comparison of Single-zone, Multi-zone and Test
Data”, SAE 2005-01-2123

3.      Heywood
JB, Internal Combustion Engine Fundamentals, Mc Graw
Hill; 1988