Download
1 / 16
160 likes | 179 Vues
A Seminar On “HCCI Engines-Opportunities & Challenges ”. MADE BY:- MR RUTVIJ PATEL. GUIDED BY:- JIGAR S.PATEL. What is HCCI???.
E N D
A Seminar On “HCCI Engines-Opportunities & Challenges” MADE BY:- MR RUTVIJ PATEL GUIDED BY:- JIGAR S.PATEL
What is HCCI??? • 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. • HCCI has characteristics of the two most popular forms of combustion used in IC engines: homogeneous charge spark ignition (gasoline engines) and stratified charge compression ignition (diesel engines).
Basics of HCCI • HCCI is an alternative piston-engine combustion process that can provide efficiencies as high as compression-ignition, direct-injection (CIDI) engines. • HCCI engines operate on the principle of having a dilute, premixed charge that reacts and burns volumetrically throughout the cylinder as it is compressed by the piston. • The important attribute of HCCI allows combustion to occur at much lower temperatures, dramatically reducing engine-out emissions of NOx. • Most engines employing HCCI to date have dual mode combustion systems in which traditional SI or CI combustion is used for operating conditions where HCCI operation is more difficult.
Advantages …… • HCCI provides up to a 15-percent 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. In fact, because peak temperatures are significantly lower than in typical spark ignited engines, NOx levels are almost negligible. Additionally, the premixed lean mixture does not produce soot. • 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.
Disadvantages…. • High in-cylinder peak pressures may cause damage to the engine. • High heat release and pressure rise rates contribute to engine wear. • The auto ignition event is difficult of 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. • Carbon monoxide (CO) and hydrocarbon (HC) pre-catalyst emissions are higher than a typical spark ignition engine, caused by incomplete oxidation (due to the rapid combustion event and low in-cylinder temperatures) and trapped crevice gases, respectively.
R&D for HCCI R&D will be required in several areas, including: • Controlling ignition timing over a wide range of speeds and loads. • Limiting the rate of combustion heat release at high-load operation. • Providing smooth operation through rapid transients. • Achieving cold-start. • Meeting emissions standards. • Research is required to understand how various fuel-injection techniques, methods for introducing EGR, and charge mixing techniques alter HCCI combustion through partial charge stratification. • R&D efforts are also needed for the development of fuel-injection hardware and other mixing control techniques that may be required to achieve the desired changes to the in-cylinder processes. • R&D efforts are needed to investigate control systems such as variable valve timing (VVT) and variable compression ratio (VCR). These controls have a strong potential for controlling the engine through transients, and switching into and out of HCCI mode. • Finally, R&D efforts are needed for the development of sensors and control algorithms for closed-loop control.
Challenges to HCCI • HCCI combustion is achieved by controlling the temperature, pressure and composition of the air/fuel mixture so that it auto ignites near top dead center (TDC) as it is compressed by the piston. • This mode of ignition is fundamentally more challenging than using a direct control mechanism such as a spark plug or fuel injector to dictate ignition timing as in SI and CIDI engines, respectively. The following describes the more significant challenges for developing practical HCCI engines for transportation. • Controlling Ignition Timing over a Range of Speeds and Loads • Extending the Operating Range to High Loads • Cold-Start Capability • Hydrocarbon and Carbon Monoxide Emissions
Recent Application of HCCI Technology • Nissan "MK" Combustion System The "Modulated Kinetics" (MK) system, developed by Nissan, incorporates in a regular CIDI engine using diesel fuel.
Controlling HCCI • HCCI is more difficult to control than other popular modern combustion engines, such as Spark Ignition (SI) and Diesel. • In an HCCI engine, however, the homogeneous mixture of fuel and air is compressed and combustion begins whenever the appropriate conditions are reached. This means that there is no well-defined combustion initiator that can be directly controlled. • Engines can be designed so that the ignition conditions occur at a desirable timing. • Several control approaches are discussed below: • Variable compression ratio • Variable induction temperature • Variable exhaust gas percentage • Variable valve actuation • High peak pressures and heat release rates • Power • Emission • Different from knock
HCCI Prototypes • As of August 2007 there were no HCCI engines being produced in commercial scale. However several car manufacturers have fully functioning HCCI prototypes. • General Motors has demonstrated Opel Vectra and Saturn Aura with modified HCCI engines. • Mercedes-Benz has developed a prototype engine called DiesOtto, with controlled auto ignition. • 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. • 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. 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.
MODELING APROACH • The framework for modeling HCCI combustion in a simple way involves partitioning the engine cycle into five stages: • Mixing of reactant and re-inducted product gases during a constant pressure, adiabatic induction process • Isentropic compression to the point where combustion initiates • Constant volume combustion to major products • Isentropic expansion to the point where the exhaust valve opens • Isentropic expansion through the exhaust valve.
CONCLUDING REMARKS • HCCI is identified as a high-risk, long-term alternative technology deserving of increased R&D support. • A high-efficiency, gasoline-fueled HCCI engine represents a major step beyond SIDI engines for light-duty vehicles. HCCI engines have the potential to match or exceed the efficiency of diesel-fueled CIDI engines without the major challenge of NOx and PM emission control or a major impact on fuel-refining capability. • HCCI engines would probably cost less than CIDI engines because HCCI engines would likely use lower-pressure fuel-injection equipment, and the combustion characteristics of HCCI would potentially enable the use of emission control devices that depend less on scarce and expensive precious metals.
REFERENCES • A REPORT TO THE U.S. CONGRESS REGARDING HCCI. • NAFTC (NATIONAL ALTERNATIVE FUEL TRAINING CONSORTIUM. • IC ENGINES: V. GANESHNA. • ASME INTERNATIONAL MECHANICAL EHGINEERING CONGRESS AND EXPOSITION.
