This document summarizes an experimental study of HCCI (Homogeneous Charge Compression Ignition) engines. HCCI engines have the potential for high efficiency and low emissions compared to spark ignition and compression ignition engines. However, controlling autoignition in HCCI engines is challenging. The document discusses various control methods for HCCI combustion including variable compression ratio, intake air heating, and variable valve timing. It also covers dual combustion modes, engine performance characteristics, recent HCCI engine prototypes, and conclusions about controlling premixed ratios in HCCI combustion for emissions and efficiency.

1. SEMINAR
on
An Experimental Study of HCCI
Engine

2. Contents
 Importance
 Working principle
 Starting of HCCI engines
 Control methods of HCCI
 Dual mode transitions
 Characteristics
 Recent developments
 Conclusion

3. HCCI
 Importance
 SI engines have very low NOx and PM emissions
 CI engines have high efficiency
 Homogeneous Charge Compression Ignition (HCCI) is
a promising alternative combustion technology with
high efficiency and lower NOx and particulate matter
emissions

4. Principle
 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
 Optical diagnostics research shows that HCCI
combustion initiates simultaneously at multiple sites
within the combustion chamber and that there is no
discernable flame propagation.

5. Comparison of SI and HCCI combustion
Spark Ignition HCCI

6. HCCI Concept

7. HCCI
 POTENTIAL
1. High efficiency, no knock limit on compression ratio.
2. Low NOx and no NOx after treatment systems required.
3. Low PM emissions, no need for PM filter.
4. HCCI provides up to a 15-percent fuel savings, while
meeting current emissions standards.
5. HCCI engines can operate on gasoline, diesel fuel, and
most alternative fuels.
6. In regards to CI engines, the omission of throttle losses
improves HCCI efficiency.

8. HCCI
 BARRIERS
1. The auto-ignition event is difficult to control,
unlike the ignition event in spark -ignition(SI)
and diesel engines which are controlled by
spark plugs and in-cylinder fuel injectors,
respectively.
2. HCCI engines have a small power range,
constrained at low loads by lean flammability
limits and high loads by in-cylinder pressure
restrictions
3. High HC and CO emissions.

9. Starting HCCI engines
 Charge does not readily auto ignite cold engines.
 Early proposal was to start in SI mode and run in
HCCI mode.
 It involves the risk of knocking and cylinder failure at
high compression ratios.
 Now intake air pre-heating with HE and burner
system allows startup in HCCI mode with
conventional starter.

10. Starting HCCI engines

11. Control methods of HCCI combustion
 The spontaneous and simultaneous combustion of
fuel-air mixture need to be controlled.
 No direct control methods possible as in SI or CI
engines.
 Various control methods are:
 Variable compression ratio
 Variable induction temperature
 Variable valve actuation

12. Control methods of HCCI combustion
 Variable compression ratio method
 The geometric compression ratio can be changed with a
movable plunger at the top of the cylinder head. This
concept used in “diesel” model aircraft engine.
 Variable induction temperature
 The simplest method uses resistance heater to
vary inlet temperature. But this method is slow
 Now FTM (Fast Thermal Management) is used. It
is accomplished by rapidly varying the cycle to
cycle intake charge temperature by rapid mixing.

13. FTM system
Rapid mixing of cool and hot intake air takes
place achieving optimal temperature as
demanded and hence better control.

14. FTM Control method
Combustion timing can be controlled by
adjusting balance of hot and cold flow

15.  Variable valve actuation (VVA)
 This method gives finer control within combustion
chamber
 Involves controlling the effective pressure ratio. It
controls the point at which the intake valve closes.
If the closure is after BDC, the effective volume
and hence compression ratio changes.
Control methods of HCCI combustion

16. Control methods of HCCI combustion

17. Dual mode transitions
 When auto-ignition occurs too early or with
too much chemical energy, combustion is too
fast and high in-cylinder pressures can
destroy an engine. For this reason, HCCI is
typically operated at lean overall fuel mixtures
 This restricts engine operation at high loads.

18. Dual mode transitions
 Practical HCCI engines will need to switch to
a conventional 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

19. SI mode transitions
 It equips VVA and spark ignition system
 Operates in HCCI mode at low to medium loads and
switches into SI mode at higher loads
 Transition is not very stable and smooth

20. DI-HCCI
 Long ignition delay and rapid mixing are required to
achieve diluted homogeneous mixture.
 Combustion noise and NOx emissions were reduced
substantially without an increase in PM.
 Combustion phasing is controlled by injection timing.
 Thus DI-HCCI proves to be promising alternative for
conventional HCCI with good range of operation.

21. Combustion characteristics

22. Emission characteristics

23. Emission characteristics

24. Emission characteristics

25. Engine performance

26. Engine performance

27. Recent developments in HCCI
 Turbo charging initially proposed to
increase power
 Challenges for turbo charging
1. Exhaust gas temperatures low (300 to 350 °c) because of
high compression ratio.
2. Post turbine exhaust gas temperature must be high enough
to preheat intake fuel-air mixture in HE.
3. Low available compressor pressure ratio.

28. Recent developments in HCCI
 Solution for turbo charging
1. Use VGT (Variable Geometry Turbine) which allows for a
greater range of turbine nozzle area, better chance to
achieve high boost.
2. Combining turbo charging and super charging may be
beneficial.
 EGR (Exhaust Gas Re-circulation) Can be
adopted for higher efficiencies and lower HC
and CO emissions.

29. Recent developments in HCCI
 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.

30. HCCI prototypes
 General Motors has demonstrated Opel Vectra and Saturn Aura
with modified HCCI engines.
 Mercedes-Benz has developed a prototype engine called Dies Otto,
with controlled auto ignition. It was displayed in its F 700 concept
car at the 2007 Frankfurt Auto Show
 Volkswagen are developing two types of engine for HCCI operation.
The first, called Combined Combustion System or CCS, is based on
the VW Group 2.0-litre diesel engine but uses homogenous intake
charge rather than traditional diesel injection. It requires the use of
synthetic fuel to achieve maximum benefit. The second is called
Gasoline Compression Ignition or GCI; it uses HCCI when cruising
and spark ignition when accelerating. Both engines have been
demonstrated in Touran prototypes, and the company expects
them to be ready for production in about 2015.

31. HCCI prototypes
 In May 2008, General Motors gave Auto Express access to a
Vauxhall 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, but
fuel economy is expected to be in the region of 43mpg with
carbon dioxide emissions of about 150 grams per kilometre,
improving on the 37mpg and 180g/km produced by the current
2.2-litre petrol engine. The new engine operates in HCCI mode
at low speeds or when cruising, switching to conventional spark-
ignition when the throttle is opened

32. Conclusions
 HCCI-DI combustion with n-heptane/diesel
dual fuel is a 3-stage combustion process
consisting of cool flame, HCCI combustion
and diffusive combustion.
Increase of premixed ratio, shortens the NTC,
increases the peak in-cylinder pressure and
temperature and rises the highest heat
release rate of HCCI combustion phase

33. Conclusions
 NOx emissions decrease firstly at low
premixed ratios and exhibit a trend of
increasing at higher premixed ratios.
 Pre-mixed ratio has no significant effect on
soot emission and the soot emission could
remain at the same level but then have a
peak value with a certain higher premixed
ratio relating to the equivalence ratio.

34. Conclusions
 The change of CO with premixed ratio is
mainly depending on whether the premixed
equivalence ratio exceeds the critical value.
UHC increases almost linearly with the
premixed ratio mainly due to the incomplete
oxidation in the boundary layer and the
crevices.

35. Conclusions
 The IMEP increases with the increase of
premixed ratio at low to medium loads.
The indicated thermal efficiency shows
deterioration at high load with large premixed
ratios.

36. Thank you