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Effects of equivalence and fuel ratios on combustion characteristics of an RCCI engine fueled with methane/n-heptane blend

  • Atie Taqizadeh
  • Omid JahanianEmail author
  • Seyed Iman Pourmousavi Kani
Article
  • 4 Downloads

Abstract

Rising fuel costs and efforts for reducing greenhouse gases have led researchers to propose optimized models of combustion which have high efficiency and low emissions. Reactivity controlled compression ignition (RCCI) engines are attractive due to their high efficiency and low NOx and soot emissions over a wide range of operating conditions. In this study, methane and n-heptane are used as low and high reactive fuels, respectively, to create suitable fuel stratification within the cylinder. Modeling is carried out by AVL FIRE coupled with a chemical kinetics solver to investigate the effects of fuel ratio, initial temperature and equivalence ratio on the combustion performance and emission characteristics. Methane/n-heptane ratios are varied according to the energy ratio of each fuel while total input energy and total equivalence ratios are fixed. By increasing methane energy ratio from 65% to 85% in the constant intake temperature and pressure, the mixture Octane number increases, which would lead to an increase in ignition delay up to 5 crank angles. As a result, IMEP would be enhanced and also NOx emission decreases because of lower combustion temperature. By increasing intake temperature, the maximum in-cylinder pressure, heat release rate and NOx emission would increase significantly while soot emission decreases, and also ringing intensity increases up to 10%. On the other hand, increasing intake temperature reduces volumetric efficiency; as a result, IMEP is reduced by 11%. Also by increasing equivalence ratio from 0.35 to 0.55 in a constant energy ratio, noticeable growth in the maximum amount of pressure and temperature could be achieved; consequently, NOx emission would increase significantly, IMEP increases by 43%, and ISFC decreases by 30%. The results indicate that these parameters have significant effects on the heavy-duty RCCI engine performance and emissions.

Keywords

RCCI Equivalence ratio Fuel ratio Methane/n-heptane blend 

Abbreviations

aBDC

After bottom dead center

aTDC

After top dead center

bBDC

Before bottom dead center

bTDC

Before top dead center

CA

Crank angle

CA50

Crank angle at which 50% of fuel is combusted

CAD

Crank angle degree

CFD

Computational fluid dynamics

CI

Compression ignition

CNG

Compressed natural gas

CO

Carbon monoxide

CO2

Carbon dioxide

EGR

Exhaust gas recirculation

ER

Equivalence ratio

EVO

Exhaust valve opening

HC

Hydrocarbon

HCCI

Homogeneous charge compression ignition

HRR

Heat release rate

IC

Internal combustion

IVC

Inlet valve closing

IMEP

Indicated mean effective pressure

ISFC

Indicated specific fuel consumption

LHV

Lower heating value

LTC

Low temperature combustion

NG

Natural gas

NO

Nitrogen monoxide

NOx

Nitrogen oxides

P

Pressure

PM

Particulate matter

PPCI

Partially premixed compression ignition

RCCI

Reactivity controlled compression ignition

RI

Ringing intensity

RPM

Revolution per minute

SI

Spark ignition

SOC

Start of combustion

SOI

Start of injection

T

Temperature

TDC

Top dead center

List of symbols

A (–)

Numerical coefficient

A0 (kJ)

Turbulence kinetic energy

D (m2 s−1)

Diffusion factor

Fs (N)

Spray force

I (kJ)

Internal energy

J (kW m−2)

Heat flux

K (–)

Turbulence tensor

M (kg)

Mass

P (kPa)

Pressure

\(\dot{Q}^{\text{c}}\) (kW)

Chemical reaction parameter

\(\dot{Q}^{\text{s}}\) (kW)

Spray parameter

U (m s−1)

Velocity

Ym (–)

Mth species mass fraction

Greek letters

δml (–)

Dirac delta function

ε (kJ)

Energy dissipation

λ (–)

Methane energy ratio

ρ (kg m−3)

density

ρm (kg m−3)

Mth species density

\(\dot{\rho }_{\text{m }}^{{ {\text{c}}}}\) (kg m−3 s−1)

Combustion parameter

\(\dot{\rho }^{\text{s}}\) (kg m−3 s−1)

Spray parameter

σ (N m−2)

Stress tensor

Notes

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Copyright information

© Akadémiai Kiadó, Budapest, Hungary 2019

Authors and Affiliations

  1. 1.Babol Noshirvani University of TechnologyBabolIran
  2. 2.University of BirjandBirjandIran

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