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Saety

Ee

Lie on board

Mobility

Competitiveness

the hee f a-

, he se f

e ees, is used here

to cause instant ignition o the whole

airuel mixture in the combustion

chamber. Whether it be a petrol ordiesel engine, this type o operation

no longer requires ignition as an

established unction. The mixture

is auto-ignited either by the

pressure and temperature o the

predetermined diesel mixture (HCCI),

or by residual burned gases (CAI).

In this case, traditional heterogeneous

hot combustion by propagation oa fame ront is replaced with overall

homogeneous combustion which is

colder (the temperature remains

less than 1,300 C). These two

points result in the absence

o ormation o soot particles

and nitrogen oxides (NOx). Eventually,

these types o engines may meet the

requirements o the Euro 4 standard,and possibly the Euro 5 standard,

without post-treatment o NOx

or particulate lters.

hcci and cai enginesKnown as HCCI (Homogeneous Charge Compression Ignition)

or diesel and CAI (Controlled Auto Ignition) or petrol, hese ees

eas a f he e ases, resulting in instantaneous

ignition o the whole mixture in the combustion chamber.

bASic FActS

RENAULTCOMMUNICATION

in SHort

Hcci And cAi EnginES work

At comprESSion rAtES

tHAt lEAd to SpontAnEouS

ignition oF tHE wHolE

mixturE. tHE rESult

iS cold combuStion in

tHE cHAmbEr, producing

vEry low lEvElS oF

Soot And nox.

h

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the e f hese ees

sss f a

afe e in the combustion

chambers which is considerably

diluted by a high concentration

o exhaust gases reinjected

or kept in the chamber.In addition, this mixture must

be perectly homogeneous.

On compression, combustion

occurs spontaneously by auto-

ignition. This phenomenon is

acilitated by the high temperature

o the gases reinjected or retained

during the premix. This type

o combustion remains dicult

to control and stability is reduced.

The engine ECU has to manage

the quantity o uel injected andthe quantity o burned gas

reinjected very accurately,

in order to preserve this stability.

This problem is currently a barrier

to petrol engines operating only

in CAI mode on a wide range

o engine speeds. Dual-mode

operation, combining traditional

injection with CAI operation, seems

a more realistic solution. However,

diesel engines work better

in HCCI mode in a signicant rangeo engine speeds. Such engines

are interesting candidates or

equipping hybrid vehicles capable

o using internal combustion in a

restricted range o engine speeds.

How doES it work?

December2008