Homogenous Charge Combustion Ignition ( HCCI) Engine

1. Homogenous Charge Combustion Ignition ( HCCI) Engine P.Ramanathan Asst Professor AMET Unviersity Chennai

2. Spark Ignition Engine- 1. Losses during gas exchanges 2. Poor Thermodynamic efficiency 3. Low combustion efficiency Compression Ignition engine 1. Emission of NOx,Soot particles and PM Demerits of existing I.C.Engine

3. Greenhouse Gases - CO2, methane Ozone ( NOx) Particles(PM) Toxics (NOx, SOx, ) - Diesel particles Diesel Engines Contribute to Multiple Air Pollutants Carbon monoxide (CO)

4. To meet demand • Reduction in exhaust emission ( CO2 & NOx) • To achieve EURO5 norms by 2015 • Higher Thermal efficiency • Energy Economy

5. soHOMOGENOUS CHARGE COMPRESSION IGNITION ENGINE IS THE EFFECTIVE WAY TO MEET THESE REQUIREMENTS

6. Why HCCI Engine ? • High efficiency and ultra low emission w.r.t conventional Diesel engine. • To achieve near zero NOx and soot emission to achieve latest Euro Norms ( E5) • To reduce fuel consumption, greenhouse gas emission. (Law of Diesel HCCI – In Germany, every one percent increase of diesel HCCI car saves 90 million liters of fuel per year. This corresponds to emission saving of some 210000 metric tones of Co2 ) Source- BOSCH news letter-GmbH- April 2008

7. What Is HCCI? • HCCI is a combustion process. HCCI is not an engine concept. HCCI must be incorporated in an engine concept. • HCCI is a low temperature chemically controlled (flameless) combustion process. • HCCI can be considered as a hybrid form between the diesel and Otto combustion process. • However combustion process is different. So there is neither Diffusion flame (as in a diesel engine) nor a flame front traveling through a premixed charge ( as in SI engine).

9. Definition • Homogeneous charge compression ignition (HCCI) is a form of internal combustion in which well-mixed fuel and oxidizer (typically air) are compressed to the point of auto-ignition, as in other forms of combustion, this exothermic reaction releases chemical energy into a sensible form that can be transformed in an engine into work and heat.

10. WORKING PRINCIPLE OF HCCI • Homogenous charge(mixture of air & fuel) should be mixed before combustion and compress to high enough temperature to achieve spontaneous ignition of the charge. • Thus HCCI is similar to SI in the sense that both processes use premixed charge and that of CI as both rely on autoignition for combustion initiation.

11. Principle of Operation • A mixture of fuel and air will ignite when the concentration and temperature of reactants is sufficiently high. • Once ignited, combustion occurs very quickly. 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.

12. Process of HCCI Working • Intake : - At first the charge is sent through the inlet manifold .The fuel easily injects into the cylinder since there is a vacuum inside the cylinder. The pressure in the cylinder is same as that of the pressure associated with the charge • Compression : - The charge inside the cylinder is compressed by the piston until the pressure and temperature rises to the peak values. The charge is divided into well-defined specks which are distributed through out the volume of the combustion chamber. Then the charge will attain its auto-ignition points.

13. Process of HCCI Working… • Combustion :- When the charge attains its auto-ignition temperature the entire mass in the cylinder will burn at once. Hence it avoids burn duration and flame propagation. Unlike in SI engine there won’t be stages of combustion. • Expansion : - As the charge burns the heat energy released will be converted into work energy and pushes the piston downwards from TDC to BDC. • Exhaust : - The exhaust gases released will be left through the exhaust manifold due to the pressure difference between the exhaust gases and the atmospheric air. The some other processes involved in the DI diesel HCCI engine processes are pilot injection, pilot fuel combustion and main fuel injection and the process goes on cyclically.

14. Methods The concentration and/or temperature can be increased by several different ways methods 1. High compression ratio 2. Pre-heating of induction gases 3. Forced induction 4. Retained or re-inducted exhaust gases

15. Advantages • HCCI provides up to a 15 - 30 % fuel savings, while meeting current emissions standards. • Since HCCI engines are fuel-lean, they can operate at a Diesel-like compression ratios (>15), thus achieving higher efficiencies than conventional spark-ignited gasoline engines. • Homogeneous mixing of fuel and air leads to cleaner combustion and lower emissions. Actually, because peak temperatures are significantly lower than in typical spark ignited engines,  • NOxlevels are almost negligible. • HCCI engines can operate on gasoline, diesel fuel, and most alternative fuels. • In regards to gasoline engines, the omission of throttle losses improves HCCI efficiency.

16. Disadvantage • 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. • HCCI engines have a small power range, constrained at low loads by lean flammability limits and high loads by in-cylinder pressure restrictions.

17. Validating the advantage • The fuel efficiency will increase from 15 to 30%. Reason: The entire mass of the charge will be distributed homogeneously through out the volume of the chamber so the entire mass will burns at once and the unburnt fuel is nearly zero percent. • The NOx is normally less than 1/500 of the CI level and no PM is generated by combustion - Reason: The residence time of exhaust gases at TDC will be reduced. The peak temperature rise rates are reduced. These two reasons will lead to reduction of NOx . The oxidation of unburnt mixture is extremely less and hence no PM is generated.

18. Validating the advantage….. • No problems of flame propagation and burn duration. - Reason: Numerous ignition points through out the mixture ensure very rapid combustion. • There won’t be Detonation(“Knocking” or “Pinging”) - Reason: In SI engines there will be auto-ignition and spark ignition from each side and leads to Detonation. But here unlike that there will be homogeneous combustion. • Very lean mixtures (low equivalence ratios (f ~ 0.3)) can be used. Reason: there won’t be any flame propogation.

19. Application • Hydrogen Internal Combustion Electric Generator • Automobiles and esp. in Heavy duty vehicles • Marine engines • Applications requiring faster rpm

20. Prototype As of 2012, there were no HCCI engines being produced in commercial scale. However, several car manufacturers have fully functioning HCCI prototypes. • In 2007-2009, General Motors has demonstrated HCCI with a modified 2.2 L Family II engine installed in Opel Vectra and Saturn Aura • Mercedes-Benz has developed a prototype engine called DiesOtto, 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. First, called Combined Combustion System or CCS, is based on the VW Group 2.0-litre diesel engine & second one is Gasoline Compression Ignition or GCI • In October 2005, the Wall Street Journal reported that Honda was developing an HCCI engine as part of an effort to produce a next generation hybrid car.

21. A step towards practical HCCI Control of the gas temperature inside the combustion chamber is vital to HCCI combustion range expansion. Nissan has developed the following technologies to deliver this: • Technology for Measuring Gas Temperature inside Combustion Chamber • 3D HCCI Simulation Technology , to control the auto-ignition timing and combustion duration. • Utilization of VVEL - To control the gas temperature inside the combustion chamber, it is necessary to change the amount of residual exhaust gas accordingly to driving conditions. Nissan uses VVEL, which allows free-control of the valve timing and lift, for both intake and exhaust valves, to control temperature by effectively using internal EGR.

22. Conclusion • Homogeneous Charge Compression Ignition (HCCI) process is the hybrid of Spark and Compression Ignition processes and superior to both. • It increases the fuel efficiency by 15 to 30% thereby saving the petroleum resources. • It can be applied for both 4-stroke and 2-stroke engine • It reduces NOx emissions by 90%. C • Complete removal of Particulate Matter(PM) • Variable compression ratios can be achieved. • No zones of combustion as in SI Process(burnt zone, unburnt zone and reaction zone). No flame propagation as in SI engines. • No burn duration as in CI engines. • No Detonation or Knocking. • Very lean mixtures can be used(f~0.3)

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