54153249 progress and recent trends in homogeneous charge compression

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!

54153249 progress and recent trends in homogeneous charge compression

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