This document discusses three advanced combustion modes for internal combustion engines: Controlled Auto Ignition Combustion (CAI), Homogenous Charge Compression Ignition (HCCI), and Premixed Charge Compression Ignition (PCCI). CAI achieves autoignition of a premixed fuel-air mixture through control of residual gases in the cylinder. HCCI autoignites a highly diluted premixed fuel-air and burned gas mixture, achieving lower emissions and temperatures than traditional diesel. PCCI involves partial premixing of fuel and air through late injection to control combustion phasing and reduce emissions over a wider range of loads compared to HCCI.

1. ADVANCES ENGINES
Ms. R Raveena B.Tech., M.Tech., PGDMM., (Ph.D)
Research Scholar
Department of Manufacturing Engineering
Annamalai University
Annamalai Nagar - 608002
Topic to be covered:
Advanced Combustion Modes of IC engines
 CAI
 HCCI
 PCCI
Submitted by

2. ADVANCED COMBUSTION MODES
 Increase more the efficiency of internal combustion engine acting on the
combustion process.
SI - Homogenous charge
 Controlled Auto Ignition Combustion (CAI)
CI - Direct injection charge
 Homogenous Charge Compression Ignition (HCCI)
 Premixed Charge Compression Ignition (PCCI)

3.  New combustion process of SI engines .
 The aim is to achieve benefits of low emissions
of NOx , particulate and small consumption of
fuels at low loads.
 Auto ignition of small mass of homogenous
and premixed mixture is produced at same
time, in a several points of combustion
chamber.
 No flame propagation but very fast combustion
of the fresh air with sharp pressure peak which
approaches the process whose acheiving
maximum thermodynamic values(instantaneous
combustion).
SI engines - Controlled Auto Ignition Combustion (CAI)

4.  To obtain high temperature required for auto
ignition of fresh air - the simple is using
residual gases retained in the cylinder at the
end of the cycle.
 Variable valve timing in engine available, the
negative value overlap (NVO) between the
opening diagram of the intake and exhaust
valve can be obtained.
SI engines - Controlled Auto Ignition Combustion (CAI)
 Varying the closing of the exhaust valve, the mass of the residual gases
retained in the cylinder is controlled.
 Mass of the fresh air is controlled by opening timiming of the inlet valve.
 CAI combustion can be safely obtained only at low loads (bmep < 0.3 Mpa)
 Traditional spark ignition combustion engines operates at higher loads .

5.  under development
 In diesel engine, a fuel element in the central
core of the spray is heated by the combination
process with high oxygen deficiency.
 At constant Φ, the element follows adiabatic
flame temperature T flame reaching area of
high particulate formation, since fuel faces
greater heat fluxes in absences of oxygen,
loosing hydrogen and forming carbon
particles.
Homogenous Charge Compression Ignition (HCCI)
 Later the fuel vapours are diluted with air, the local tempearture are so
high that NOX are largely produced.

6.  The new HCCI combustion process aim to prepare in the cylinder the gaseous
fuel and premixed fuel mixture highly diluted in air, recycle burned
gases.Finally, all this mixture is forced to auto ignite nearly at same time,
with no flame front gradually propagating to the charge.
 There is no risk in the particulate formation.
 The combustion process, the mean temperature of the reacting charge is
lower than local temperature of the diffusive flames.
 The production of the NOX is definitely low.
Homogenous Charge Compression Ignition (HCCI)

7. Advantages:
• High thermodynamic efficiency
• Engine load is controlled by varying amount of injected fuel
Charge inhomogenity:
• ineffective mixing of air & Fuel (Composition)
• ineffective mixing of fresh charge and hot residual gases (Temperature)
Homogenous Charge Compression Ignition (HCCI)

8.  PCCI combustion is a practical way of achieving low NOx and low soot in CI
engines. NOx can be reduced by reducing combustion temperature.
 The engine- out soot reflects the balance between soot that is formed and the
soot that is oxidised within the cylinder.
 In HCCI engiines very lean mixtures ensure low NOx and low soot- indeed in
HCCI engines as equivalence ratio (load at a given speed)increases, NOx (and
heat release rate) will increase and will eventually be too high. Also, HCCI
engines have no in-cycle control over combustion phasing.In diesel (practical
CI) engines. NOx can be reduced by using EGR . However, if you use EGR,
soot oxidation is inhibited and engine-out soot will increase.
Premixed Charge Compression Ignition (PCCI)

9.  The fuel and oxygen should be "premixed enough" to get these benefits but must not be
fully premixed. The inhomogeneity in the cylinder achieved with late injection allows the
engine to be run at conditions where HCCI combustion would not be possible.
 In premixed chage compressed ignition
combustion, if the final fuel injection, which
controls combustion phasing, is completed
sufficiently before combustion starts (high
ignition delay), soot formation can be
avoided in the first place and EGR can be
used to control NOx.With conventional
diesel fuel PCI combustion is possible only
at very low loads. Increasing the injection
pressure or reducing the cetane number of
the fuel makes PCI combustion easier.
Premixed Charge Compression Ignition (PCCI)