54153249 progress and recent trends in homogeneous charge compression
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8/6/2019 54153249 Progress and Recent Trends in Homogeneous Charge Compression
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Progress and Recent Trends in
Homogeneous Charge Compression
Ignition (HCCI) Engines
Visakh R
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CONTENTS
What is HCCI? Importance of HCCI
Pioneering Researches in HCCI
Challenges Faced in HCCI
Methodologies Used in Investigation of HCCI
Evolution In Control Strategies
Various Control Strategies Explained
Dual Mode Transitions
Recent Developments
HCCI Prototypes Conclusion
Reference
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What Is HCCI?
An HCCI engine is a mix of both conventional spark-ignition anddiesel compression ignition technology.
HCCI is characterized by the fact that the fuel and air are mixed
before combustion starts and the mixture auto-ignites as a result of
the temperature increase in the compression stroke.
The resulting spontaneous burn produces a flameless energyrelease in a large zone almost simultaneously -- very different than
the spark/gasoline burn or the compression/diesel burn.
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IMPORTANCE OF HCCI Homogeneous Charge Compression Ignition (HCCI) is a promising
alternative combustion technology with high efficiency and lowerNOx and particulate matter emissions.
It can operate using a variety of fuels -- gasoline, diesel, natural gas,
biofuels, hydrogen.
HCCI combustion incorporates the advantages of both spark ignition
(SI) engines and compression ignition direct injection (CIDI)engines.
However, there are still tough challenges in the successful operation
of HCCI engines, such as controlling the combustion phasing,
extending the operating range, and high unburned hydrocarbon and
CO emissions. Massive research throughout the world has led to great progress in
the control of HCCI combustion. The first thing paid attention to is
that a great deal of fundamental theoretical research has been
carried out.
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Pioneering Researches In HCCISl.
NoAUTHOR Aim \ Input Output Result
1Onishi et
al
Investigate gasoline
systems to increase
combustion stability of
two stroke engines.
Stable HCCI
combustion
between low and
high loads at CR
7.5:1
Reduction in
emissions and
improved fuel
economy
2Noguchi et
al
Spectroscopy onHCCI combustion,
experimental work on
two stroke engine
Species relatedto low temp auto
ignition were
found like O &
HO2 radicals
Ignition atnumerous
points & no
discernable
flamefront.
3 Ryan et alInvestigate Diesel
fueled HCCI. UsedPort fuel injection.
Premature
ignition andknocking;
Unburned HC
emissions high;NOx reduced.
4Mingfa
yao et al
Evaluate the progress
and current trends
Present state of
research
revealed
New strategies
and challenges
defined
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Challenges Faced by HCCI
Difficulty in Combustion phasing control.
High levels of Noise, UHC and CO emissions
Operation Range
Cold Start
Homogeneous Mixture Preparation
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Methodologies used in investigation of HCCI
Numerical Simulation
1. Zero Dimensional single zone model
2. Quasi Dimensional multi zone model
3. One Dimensional engine cycle
4. Multi Dimensional CFD
Optical Diagnostics
1. For In cylinder mixture formation2. For Combustion Process
3. For Emission Process
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Chemical Kinetics Model
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Multi Dimensional CFD with Chemical Kinetics Models
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Optical Diagnostics For In Cylinder Mixture Formation
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Optical Diagnostics For Combustion Process
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Effect Of fuels, additives and fuel modifications on
HCCI chemical kinetics process
One of the advantages of HCCI combustion is its intrinsic fuel
flexibility. HCCI combustion has little sensitivity to fuel
characteristics such as lubricity and laminar flame speed. Fuels with
any octane or cetane number can be burned, although the operating
conditions must be adjusted to accommodate different fuels, which
can impact efficiency
HCCI combustion can be controlled and the HCCI operating range
can be extended by burning different octane number fuel at different
engine modes, i.e. burning low/high octane number fuel at low/ high
load mode respectively. There exists an optimum octane number
that achieves the highest indicated thermal efficiency at differentengine load.
Stratification Combustion- inhomogenity is an important path to
achieve clean & high efficiency combustion in engines.
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Contd
Ignition promoters and inhibitors are available.
Exhaust Gas Recirculation (EGR) into intake is the most
practical means of controlling charge temperature in an
HCCI engine. EGR enhances combustion, control heat release, delay
auto-ignition timing, and thus lower peak cylinder
pressure.
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Evolution In Control Strategies
The spontaneous and simultaneous combustion of
fuel-air mixture need to be controlled.
No direct control methods possible as in SI or CI
engines.
In Diesel HCCI, it is difficult to prepare homogeneous
mixture because of the lower volatility, higherviscosity and lower resistance to auto ignition of
diesel fuel.
In Gasoline HCCI, high octane rating of the fuel
means it needs high ignition temperature, whichbrings the difficulty of auto-ignition by compression.
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Control Methods
Various control methods are:
Variable compression ratio
Exhaust Gas Recirculation
Variable valve actuation
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Control Methods Explained
Variable compression ratio method (VCR) The geometric compression ratio can be changed with
a movable plunger at the top of the cylinder head.
VCR changes in-cylinder pressure and density, which
can produce effects on auto-ignition of fuel, and bywhich the in-cylinder temperature is controlled.
Exhaust Gas Recirculation (EGR)
EGR mixes with fresh air as diluter can lead to
increase of specific heat capacity in the cylinder.Hence, Ignition delay becomes longer.
In addition, flame temperature after ignition decrease,
which is beneficial in reducing NOx emissions.
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Control Methods Explained
Variable valve actuation (VVA)
This method gives finer control within combustion
chamber
Involves controlling the effective pressure ratio. Itcontrols the point at which the intake valve closes. If
the closure is after BDC, the effective volume and
hence compression ratio changes
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Dual Mode Transitions
Practical HCCI engines will need to switch to aconventional SI or diesel mode at very low and
high load conditions due to dilution limits.
Two modes:
HCCI-DI dual mode HCCI-SI dual mode
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Recent Developments
EGR (Exhaust Gas Re-circulation) Can beadopted for higher efficiencies and lower HC
and CO emissions.
The exhaust has dual effects on HCCI
combustion. It dilutes the fresh charge, delaying ignition and
reducing the chemical energy and engine work.
Reduce the CO and HC emissions
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HCCI Prototypes
General Motors has demonstrated Opel Vectra and SaturnAura with modified HCCI engines.
Mercedes-Benz has developed a prototype engine called DiesOtto, with controlled auto ignition. It was displayed in its F 700concept car at the 2007 Frankfurt Auto Show
Volkswagen are developing two types of engine for HCCIoperation. The first, called Combined Combustion System orCCS, is based on the VW Group 2.0-litre diesel engine butuses homogenous intake charge rather than traditional dieselinjection. It requires the use of synthetic fuel to achievemaximum benefit. The second is called Gasoline
Compression Ignition or GCI; it uses HCCI when cruising andspark ignition when accelerating. Both engines have beendemonstrated in Touran prototypes, and the company expectsthem to be ready for production in about 2015.
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HCCI Prototypes
In May 2008, General Motors gave Auto Express access to aVauxhall Insignia prototype fitted with a 2.2-litre HCCI engine,which will be offered alongside their ecoFLEX range of small-capacity, turbocharged petrol and diesel engines when the car
goes into production. Official figures are not yet available, butfuel economy is expected to be in the region of 43mpg withcarbon dioxide emissions of about 150 grams per kilometer,improving on the 37mpg and 180g/km produced by thecurrent 2.2-litre petrol engine. The new engine operates inHCCI mode at low speeds or when cruising, switching to
conventional spark-ignition when the throttle is opened
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Conclusion
Four main results from pioneering investigations: HCCI combustion demonstrates a strong potential to
improve thermal efficiency of gasoline fuelled engines and
reduce NOx and soot emissions of diesel fuelled engines.
Chemical kinetics has a dominating role in HCCI
Various challenges to HCCI are to be overcome HCCI concept can be extended to all new engine
combustion modes achieving high efficiency and low
emissions.
Numerical Simulation has become a powerful tool in
realizing HCCI and seeking control strategies for HCCI, andhas higher flexibility and lower cost compared with engine
experiments.
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Contd HCCI can be applied to a variety of fuels types and the choice
of fuel will have a significant impact on both engine designand control strategies.
Utilizing charge inhomogenity is an important path to achieve
clean and high efficiency combustion in engines. Stratification
strategy has the potential to extend HCCI operation range to
higher loads.
Application of Optical Diagnostics has greatly accelerated
developments in many aspects of HCCI research, including
combustion processes and emissions formation.
Essential factor needed to achieve diesel fuelled HCCIcombustion is mixture control. For gasoline fuelled HCCI, it is
by the use of large levels of residual exhaust gases.
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REFERENCE Progress and recent trends in homogeneous charge
compression ignition engines Ming Yao,Zhaolei Zheng,Haifeng Liu
A parametric study on the emissions from an HCCIalternative combustion engine resulting from the auto-ignitionof primary reference fuels Hatim Machrafi , Simeon
Cavadias, Jacques Amouroux. An experimental study of HCCI-DI combustion and emissions
in a diesel engine with dual fuel Junjun Ma, Xingcai L, LibinJi, Zhen Huang
http://www-erd.llnl.gov/FuelsoftheFuture/pdf_files/hccirtc.pdf
http://www.ecogeek.org/component/content/article/1631 http://www.greencarcongress.com/2004/05/keep_an_eye_on_
.html
wikipedia.org
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THANK YOU!
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