A CASE STUDY IN HOMOGENEOUS CHARGE COMPRESSION IGNITION ENGINES

Transcription

1 A CASE STUDY IN HOMOGENEOUS CHARGE COMPRESSION IGNITION ENGINES Sreejith C 1, Abhijit Roy 2, Abhishek Samanta 3, Indira Ghosh 4 and Ragul G 5 1 Department of Automobile Engineering, Nehru College of Engineering & Research Centre, Thrissur, India 2,3,4,5 Department of Mechanical Engineering, Budge Budge Institute of Technology, Kolkata, India Abstract This paper reports an investigation that was carried out in a HCCI has characteristics of the two most popular forms of combustion used in SI (spark ignition) engines- homogeneous charge spark ignition (gasoline engines) and CI engines: stratified charge compression ignition (diesel engines). As in homogeneous charge spark ignition, the fuel and oxidizer are mixed together. However, rather than using an electric discharge to ignite a portion of the mixture, the density and temperature of the mixture are raised by compression until the entire mixture reacts spontaneously. Stratified charge compression ignition also relies on temperature and density increase resulting from compression, but combustion occurs at the boundary of fuel-air mixing, caused by an injection event, to initiate combustion. The defining characteristic of HCCI is that the ignition occurs at several places at a time which makes the fuel/air mixture burn nearly simultaneously. There is no direct initiator of combustion. This makes the process inherently challenging to control. However, with advances in microprocessors and a physical understanding of the ignition process, HCCI can be controlled to achieve gasoline engine-like emissions along with diesel engine-like efficiency. In fact, HCCI engines have been shown to achieve extremely low levels of Nitrogen oxide emissions (NOx) without an after treatment catalytic converter. The unburned hydrocarbon and carbon monoxide emissions are still high (due to lower peak temperatures), as in gasoline engines, and must still be treated to meet automotive emission regulations. Recent research has shown that the use of two fuels with different reactivities (such as gasoline and diesel) can help solve some of the difficulties of controlling HCCI ignition and burn rates. RCCI or Reactivity Controlled Compression Ignition has been demonstrated to provide highly efficient, low emissions operation over wide load and speed ranges. Index Terms Homogeneous charge compression Ignition, Gasoline Engines, Diesel Engines, Variable Compression ratio. I. INTRODUCTION 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). As in homogeneous charge spark ignition, the fuel and oxidizer are mixed together. However, rather than using an electric discharge to ignite a portion of the mixture, the concentration and temperature of the mixture are raised by compression until the entire mixture reacts simultaneously. Stratified charge compression ignition also relies on temperature increase and concentration resulting from compression, but combustion occurs at the boundary of fuel-air mixing, caused by an injection event, to initiate combustion. In SI engines, large cycle-to-cycle variations occur since the early flame development varies considerably due to mixture in homogeneity in the vicinity of the spark plug. With HCCI, cycle-to-cycle variations of combustion are very small, since combustion initiation takes place at many points at the same time. This defining characteristic of HCCI makes the fuel/air mixture burn nearly simultaneously. There is no direct initiator of combustion. This makes the process inherently challenging to control. However, with advances in microprocessors and a physical understanding of the ignition process, HCCI can be controlled to achieve gasoline engine-like emissions along with diesel engine-like efficiency. In fact, HCCI engines have been shown to achieve extremely low levels of Nitrogen oxide emissions (NOx) without after treatment catalytic converter. The unburned hydrocarbon and carbon monoxide emissions are still high (due to lower peak temperatures), as in gasoline engines, and must still be treated to meet automotive emission regulations. The IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 158

2 homogeneous charge compression ignition (HCCI) engine has caught the attention of automotive and diesel engine manufacturers worldwide because of its potential to rival the high efficiency of diesel engines while keeping NOx and particulate emissions extremely low. However, researchers must overcome several technical barriers, such as controlling ignition timing, reducing unburned hydrocarbon and carbon monoxide emissions, extending operation to higher loads, and maintaining combustion stability through rapid transients. HCCI engines can operate using a variety of fuels. In the near term, the application of HCCI to automotive engines will likely involve mixed-mode combustion in which HCCI is used at low-to-moderate loads and standard spark-ignition (SI) combustion is used at higher loads. other conventional combustion concepts like spark or compression ignition. In the HCCI engine homogeneous mixture is created and it depends on solution in the intake system or inside the cylinder. Homogeneous charge or air is drawn into the cylinder during suction stroke and compressed to high enough temperature and pressure. To achieve homogeneous spontaneous ignition of the charge preferable near TDC, high intake temperature and the high compression ratio are required. In contrast to SI and CI engines HCCI combustion lacks from the flame propagation. Combustion initiation occurs simultaneously at whole volume of combustion chamber and burns at the same time. II. MAIN CHALLENGES AND SOLUTIONS Major Challenges in automobile sector are Emission (NOx & Soot) and Fuel Economy 2.1 Emission NOx is a generic term for oxides of nitrogen, a mixture of nitric oxide (NO) and nitrogen dioxide (NO2), which are by-products of combustion at high temperatures, such as those which occur in an engine cylinder. NOx is a leading cause of, or contributing factor to, a range of respiratory diseases such as asthma, emphysema and bronchitis, conditions which can lead to premature death. The formation of ozone, which can result in lung damage, is another major adverse effect of NOx emissions. 2.2 Fuel Economy Fuel economy is the energy efficiency of a particular vehicle, is given as a ratio of distance travelled per unit of fuel consumed. Fuel economy is a major problem due to increase in population and scarcity of oil. Some of the solutions to these challenges are: Hybrid Vehicles Fuel Cells HCCI Engines GDI Engine III. PRINCIPLE OF WORKING The HCCI concept, which is proposed as an ultimate method of lean burn, is completely different from Fig.1. Photo sequence of HCCI combustion, based on 20 images per degree CA In the fig.1 it can be seen that the combustion starts in almost whole volume of combustion chamber two Crank Angle Degrees before TDC (CAD-02). After combustion initiation the temperature and pressure rapidly increase and whole bulk of fuel burns simultaneously within a few crank angles (CAD-00 to CAD+03). Because the whole mixture burns almost homogeneously unstable flame propagation is avoided. The HCCI non flame combustion process can be described as a premixed distributed reaction zone. On the contrary to the SI engines where large cycle to cycle variation occur, since the early flame development varies considerably due to mixture inhomogeneity in the vicinity of the spark plug, HCCI cycle to cycle variations of combustion are very small. Also in contrast to contemporary engines HCCI fast IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 159

3 combustion causes very high and fast heat and pressure release. Under some conditions where enough power was generated p max exceeded 200 bars what is considered to be the critical limit for engine mechanisms. To avoid so fast combustion highly diluted mixture must be used. Fig.2.SI, CI and HCCI Engine Comparison 3.1 Method of Operation The mixture will spontaneously ignite when it reaches its auto-ignition temperature as a result of the temperature increase in the compression stroke. A mixture of fuel and air will ignite when the concentration and temperature of reactants is sufficiently high. The concentration and/or temperature can be increased by several different ways: High compression ratio Pre-heating of induction gases Forced induction Retained or re-inducted exhaust gases Fig.3. HCCI Concept IV. MODES OF OPERATION 4.1 Different Modes of Operation Combustion start is controlled externally in both SI and CI engine, while in HCCI; combustion start is dependent only on the thermo-chemical conditions inside the cylinder. As the driver steps further on the accelerator, more fuel is introduced into the engine and hence higher temperature and pressure build up inside the cylinder, which causes the combustion to start earlier. Unfortunately, in the lower load area, combustion starts too late to have a sustainable combustion. This is called misfire. In contrast, at higher loads, the combustion starts too early causing a large heat release rate which causes a phenomenon called combustion knock. This limits the operating range into a narrow window. So HCCI engines will need to switch to a conventional SI or diesel mode at very low and high load conditions due to dilution limits. 4.2 HCCI-DI DUAL MODE A dual combustion system could potentially overcome the limits of low-load operations and allow for a gradual transition between the conventional DI mode at high load and the HCCI external mixture formation at idle and low load. Using an automotive common rail Diesel engine, a rapid prototyping ECU is used to control the direct injection system, varying the number of injections, rail pressure, timings and fuel quantities. The ECU also controls the quantity of fuel atomized in the intake manifold, as well as the EGR dilution and charge temperature. 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. 4.3 HCCI-SI DUAL MODE Another concept to overcome the disadvantages of HCCI is to use HCCI / SI dual mode combustion. Equipped with the VVA and spark ignition system, the HCCI/SI dual mode engine is able to operate in HCCI mode at low to medium loads and it can switch into SI mode to meet the large power output requirements. However the mode transition, especially from HCCI IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 160

4 to SI, is not very stable and smooth so that more improvements would be needed on the control strategies to diminish the cycle-to-cycle variation. Generally, this dual mode engine combines the HCCI and SI together to achieve the best performance. V. RESULTS USING DIFFERENT FUELS 5.1 Gasoline Gasoline has multiple advantages as an HCCI fuel. Gasoline also has a high octane number, which allows the use of reasonably high compression ratios in HCCI engines. Actual compression ratios for gasoline-fueled HCC engine data vary from 12:1 to 21:1 depending on the fuel octane number, intake air temperature, and the specific engine used (which may affect the amount of hot residual naturally retained). This compressionratio range allows gasoline-fuelled HCCI engines to achieve relatively high thermal efficiencies (in the range of diesel-fueled CIDI engine efficiencies). A potential drawback to higher compression ratios is that the engine design must accommodate the relatively high cylinder pressures that can result, particularly at high engine loads. Additional advantages of gasoline include easy evaporation, simple mixture preparation, and a ubiquitous refuelling infrastructure 5.2 Diesel Fuel Diesel fuel auto ignites rapidly at relatively low temperatures but is difficult to evaporate. To obtain diesel-fuel HCCI combustion, the air-fuel mixture must be heated considerably to evaporate the fuel. The compression ratio of the engine must be very low (8:1 or lower) to obtain satisfactory combustion, which results in a low engine efficiency. Alternatively, the fuel can be injected in-cylinder, but without air preheating, temperatures are not sufficiently high for diesel-fuel vaporization until well up the compression stroke. This strategy often results in incomplete fuel vaporization and poor mixture preparation, which can lead to particulate matter and NOx emissions. However, one concept for direct injection of diesel fuel, involving late injection (after TDC) with high swirl, has been successful at thoroughly vaporizing and mixing the fuel before ignition at light loads. This mode of operation is used in the Nissan MK engine, to be discussed in the next sub-section. In addition, diesel fuel has an extensive refueling infrastructure. 5.3 Propane Propane is an excellent fuel for HCCI. High efficiencies can be achieved with propane-fueled HCCI engines because propane has a high octane number (105). Because propane is a gaseous fuel, it can be easily mixed with air. Some infrastructure also exists for propane. Because it can be maintained as a liquid at moderate pressures, the amount of fuel that can be stored onboard a vehicle is comparable to what can be stored for typical liquid fuels. 5.4 Natural Gas Because natural gas has an extremely high octane rating (about 110), natural gas HCCI engines can be operated at very high compression ratios (15:1 to 21:1), resulting in high efficiency. However, similar to gasoline or propane, the engine design must accommodate the relatively high cylinder pressures that can result. Natural gas is widely available throughout the U.S. VI. CONTROLLING COMBUSTION IN HCCI 6.1 Difficulty Controlling HCCI is a major hurdle to more widespread commercialization. HCCI is more difficult to control than other popular modern combustion engines, such as Spark Ignition (SI) and Diesel. In a typical gasoline engine, a spark is used to ignite the pre-mixed fuel and air. In Diesel engine, combustion begins when the fuel is injected into compressed air. In both cases, the timing of combustion is explicitly controlled. 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. An engine can be designed so that the ignition conditions occur at a desirable timing. However, this would only happen at one operating point. The engine could not change the amount of work it produces. This could work in a hybrid vehicle, but most engines must modulate their output to meet user demands dynamically. To achieve dynamic operation in an HCCI engine, the control system must change the conditions that induce combustion. Thus, the engine must control either the compression ratio, IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 161

5 inducted gas temperature, inducted gas pressure, fuelair ratio, or quantity of retained or re inducted exhaust. The approaches suggested for control are Variable compression ratio Variable induction temperature Variable valve actuation Variable exhaust gas percentage Variable fuel ignition quality 6.2 Variable Compression ratio There are several methods for modulating both the geometric and effective compression ratio. The geometric compression ratio can be changed with a movable plunger at the top of the cylinder head. The effective compression ratio can be reduced from the geometric ratio by closing the intake valve either very late or very early with some form of variable valve actuation. Both of the approaches mentioned above require some amounts of energy to achieve fast responses. Additionally, implementation is expensive. Control of an HCCI engine using variable compression ratio strategies has been shown effective. 6.3 Variable Induction Temperature In HCCI engines, the auto ignition event is highly sensitive to temperature. Various methods have been developed which use temperature to control combustion timing. The simplest method uses resistance heaters to vary the inlet temperature, but this approach is slow (cannot change on a cycle-to-cycle basis). Another technique is known as fast thermal management (FTM). It is accomplished by rapidly varying the cycle to cycle intake charge temperature by rapidly mixing hot and cold air streams. It is also expensive to implement and has limited bandwidth associated with actuator energy. Fig.4.FTM System 6.4 Variable Valve Actuation Variable valve actuation (VVA) has been proven to extend the HCCI operating region by giving finer control over the temperature-pressure-time history within the combustion chamber. VVA can achieve this via two distinct methods. Controlling the effective compression ratio: A variable duration VVA system on intake can control the point at which the intake valve closes. If this is retarded past bottom dead center (BDC), then the compression ratio will change, altering the in-cylinder pressure-time history prior to combustion. Controlling the amount of hot exhaust gas retained in the combustion chamber: A VVA system can be used to control the amount of hot internal exhaust gas recirculation (EGR) within the combustion chamber. This can be achieved with several methods, including valve re-opening and changes in valve overlap. By balancing the percentage of cooled external EGR with the hot internal EGR generated by a VVA system, it may be possible to control the in-cylinder temperature. While electro-hydraulic and cam less VVA systems can be used to give a great deal of control over the valve event, the component for such systems is currently complicated and expensive. Mechanical variable lift and duration systems, however, although still being more complex than a standard valve train, are far cheaper and less complicated. If the desired VVA characteristic is known, then it is relatively simple to configure such systems to achieve the necessary control over the valve lift curve. 6.5 Variable Exhaust Gas Percentage Exhaust gas can be very hot if retained or re-inducted from the previous combustion cycle or cool if recirculate through the intake as in conventional EGR systems. The exhaust has dual effects on HCCI combustion. It dilutes the fresh charge, delaying ignition and reducing the chemical energy and engine work. Hot combustion products conversely will increase the temperature of the gases in the cylinder and advance ignition. 6.6 Variable Fuel Ignition Quality Another means to extend the operating range is to control the onset of ignition and the heat release rate by manipulating the fuel itself. This is usually carried out by adopting multiple fuels and blending them "on the fly" for the same engine. Examples could be IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 162

6 blending of commercial gasoline and diesel fuels, adopting natural gas or ethanol. This can be achieved in a number of ways: Blending fuels upstream of the engine: Two fuels are mixed in the liquid phase, one with low resistance to ignition (such as diesel fuel) and a second with a greater resistance (gasoline), the timing of ignition is controlled by varying the compositional ratio of these fuels. Fuel is then delivered using either a port or direct injection event. Having two fuel circuits: Fuel A can be injected in the intake duct (port injection) and Fuel B using a direct injection (in-cylinder) event, the proportion of these fuels can be used to control ignition, heat release rate as well as exhaust gas emissions. A. Power Output In both a spark ignition engine and diesel engine, power can be increased by introducing more fuel into the combustion chamber. These engines can withstand a boost in power because the heat release rate in these engines is slow. However, in HCCI engines the entire mixture burns nearly simultaneously. Increasing the fuel/air ratio will result in even higher peak pressures and heat release rates. In addition, many of the viable control strategies for HCCI require thermal preheating of the charge which reduces the density and hence the mass of the air/fuel charge in the combustion chamber, reducing power. These factors make increasing the power in HCCI engines challenging. One way to increase power is to use fuels with different autoignition properties. This will lower the heat release rate and peak pressures and will make it possible to increase the equivalence ratio. Another way is to thermally stratify the charge so that different points in the compressed charge will have different temperatures and will burn at different times lowering the heat release rate making it possible to increase power. A third way is to run the engine in HCCI mode only at part load conditions and run it as a diesel or spark ignition engine at full or near full load conditions. Since much more research is required to successfully implement thermal stratification in the compressed charge, the last approach is being studied more intensively. B. Emissions from HCCI Engine Because HCCI operates on lean mixtures, the peak temperatures are lower in comparison to spark ignition (SI) and Diesel engines. The low peak temperatures prevent the formation of NOx. This leads to NOx emissions at levels far less than those found in traditional engines. However, the low peak temperatures also lead to incomplete burning of fuel, especially near the walls of the combustion chamber. This leads to high carbon monoxide and hydrocarbon emissions. An oxidizing catalyst would be effective at removing the regulated species because the exhaust is still oxygen rich. VII. 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, 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. HCCI engines may be lower cost due to lack of injection system etc. VIII. 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 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. Carbon monoxide (CO) and hydrocarbon (HC) pre-catalyst emissions are higher than a typical spark ignition engine, caused by incomplete IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 163

7 oxidation (due to the rapid combustion event and low in-cylinder temperatures) and trapped crevice gases, respectively. Extending the Operating Range to High Load Cold-Start Capability IX. RESEARCH 9.1 Introduction Ford, General Motors (GM), and Cummins Engine Company have been performing research on HCCI combustion. Ford motor company has an active research program in HCCI combustion. Researchers are using optical diagnostics in single-cylinder engines to explore viable HCCI operating regimes and to investigate methods of combustion control. In addition, chemical kinetic and cycle simulation models are being applied to better understand the fundamentals of the HCCI process and to explore methods of implementing HCCI technology.gm, at a research level, is evaluating the potential for incorporating HCCI combustion into engine systems. This work includes assessing the strengths and weaknesses of HCCI operation relative to other advanced concepts, assessing how best to integrate HCCI combustion into a viable power train, and the development of appropriate modeling tools. Work is focused on fuels, combustion control, combustion modeling, and mode transitioning between HCCI and traditional SI or CI combustion. GM is also supporting HCCI work at the university level. Cummins has been researching HCCI for almost 15 years. Industrial engines run in-house using HCCI combustion of natural gas has achieved remarkable emission and efficiency results The main areas requiring R&D are outlined below Ignition Timing Control Heat release rate Engine Cold-Start Multi-Cylinder Engine Effects Fuel System Engine Control Strategies and Systems 9.2 Ignition Timing Control R&D is needed to develop control methods for HCCI engines in order to overcome the challenge of maintaining ignition timing as load and speed are varied. Maintaining optimal ignition timing is more challenging for HCCI engines than for conventional engines because no positive mechanism, such as spark or fuel-injection, determines ignition timing. In HCCI engines, ignition timing is determined by the chemical kinetic reaction rates of the mixture, which are controlled by time, temperature, and mixture composition. Of these parameters, ignition timing is most sensitive to temperature. As engine speed and load (time and mixture) are varied, the ignition timing will also vary, unless the charge temperature is adjusted to compensate. The amount of compensation required is a strong function of fuel type, with onestage-ignition fuels (e.g. gasoline) requiring much less compensation for changes in speed and load than twostage-ignition fuels (e.g. diesel). Perhaps the most straightforward way to control charge temperature in an HCCI engine is to add a variable amount of hot EGR to the intake; however, the response is slow, and transients are not handled well. Alternatively, varying the temperature by mechanical variation of the compression ratio (VCR) has recently been demonstrated as an excellent way of controlling HCCI ignition timing. 9.3 Heat Release Rate R&D is needed to develop methods to slow the rate of combustion in HCCI engines at high engine loads to prevent excessive noise and engine damage. Two solutions are as follows: First, on a shorter time horizon, at high loads the engine could switch over and run as a conventional SI or CIDI engine. SI operation has advantages for control of NOx emissions, and gasoline-like fuels offer additional advantages. On the other hand, CIDI operation has the advantage of high efficiency. Conversion to SI operation may require reducing the compression ratio, which would be straightforward for an engine equipped with a VVT or VCR system. Second, the charge temperature and/or mixture could be partially stratified to smooth out the heat release rate. Because even small variations in intake temperature (~10 C) can significantly alter HCCI ignition timing, thermal stratification is a feasible means of spreading out the heat release. 9.4 Engine Cold Start R&D is needed to develop concepts to overcome the challenge of ignition in cold HCCI engines without compromising the warm engine performance. Past IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 164

8 research has focused on warm-engine HCCI operation, and little, if any, research has been conducted to address the issue of cold start. HCCI combustion is strongly dependent on the charge temperature. During cold-start, the fuel/air charge receives no preheating from the intake manifolds and ports, and heat transfer from the compressed charge to the cold combustion chamber walls is high. The combination of these effects can significantly reduce the compressed-gas temperature and prevent an HCCI engine from firing. Three solutions appear possible. First, the engine could be started as a conventional spark-ignition (SI) engine, and then switched to HCCI mode after a short warm-up. This scheme would likely require the compression ratio to be reduced during the SI, warm-up operation, which could be readily accomplished on an engine equipped with a VVT or VCR system to handle transients. VVT has the added benefit of allowing the hot residual to be retained from the previous cycle; thereby allowing a more rapid transition to HCCI. (The engine could also be started as a CIDI engine without any compression-ratio adjustment, but gasoline-like fuels offer more advantages). Second, the engine could be started in HCCI mode by increasing the compression ratio during cold start, with a VVT or VCR system. Third, a glow plug could be used to assist HCCI ignition until the engine warms up. Combinations of these systems might also be used. 9.5 Multi Cylinder Engine Effects R&D is needed to develop intake and exhaust manifold designs for multi-cylinder engines to overcome the challenge of maintaining strict uniformity of the inlet and exhaust flows of each cylinder to assure smooth engine operation. In multicylinder engines, manifold wave dynamics can cause small differences in the amount of hot residual combustion products remaining and the amount of fresh charge delivered to the various cylinders. 9.6 Fuel System R&D is necessary to develop a fuel delivery system because it is a key enabling technology to overcome the challenge of maintaining proper ignition timing, smooth combustion rates, and low emissions over the operating range of the engine. Various types of fuel systems have been proposed including port fuel injectors, DI fuel injectors similar to those designed for SI engines, DI diesel engine injectors, and combinations of these injectors. Each type has advantages for different operating regimes and fuel types. 9.7 Engine Control Strategies R&D is necessary to develop a methodology for feedback and closed-loop control of the fuel and air systems to keep the combustion optimized over the speed and load range of the engine in a production vehicle. Control mechanisms, sensors, and appropriate control algorithms are key enabling technologies for practical HCCI engines. VVT and/or VCR systems have a strong potential for controlling HCCI engines and addressing many of the important issues such as ignition timing, cold-start, transients, fuel type, and switching into or out of SI mode X. FUTURE OF HCCI ENGINE The future of HCCI looks promising especially with partial HCCI mode. Major companies such as GM, Mercedes-Benz, Honda, and Volkswagen have invested in HCCI research. Table.1.Investment Details Company General Motors Mercede s Volkswa gen Satur n- Aura Opel- Vectr a Diesotto Toura n Technolo gy phcci phcci 2015 phcci CCS 2015 Ford phcci 2015 Estimated Year of Commercializat ion Test Vehicle is on road Test Vehicle is on road Because HCCI works best at relatively constant, partial-load conditions, the HCCI engines being developed right now are actually combination engines that can run as either spark ignition or HCCI. At higher IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 165

9 speeds or loads, the engine runs as a normal SI type and then transitions to HCCI when the conditions warrant. The control software required to reliably detect when to operate in either mode as well as transitioning between modes is extremely complex and requires a lot of development. Most of the hardware necessary required to produce HCCI/SI engines exists now and the main stumbling block is getting reliable, cost effective cylinder pressure sensors. All of this technology results in an engine that approaches the efficiency of diesel engines at a significantly lower cost. An HCCI engine provides a fifteen percent boost in fuel economy and reduced emissions compared to a conventional SI engine using pretty much the same exhaust after-treatment systems. For the first media sampling of HCCI, GM provided an automatic transmission-equipped Saturn Aura and five speed manual Opel Vectra. Both cars had the same 2.2L Ecotec four cylinders modified to operate in HCCI mode at speeds up to 55 mph and partial loads. A display mounted on top of the dashboard shows a map of engine speed and fuel mass and indicates when the engine is in SI or HCCI mode. On the test loop that we were able to drive, the transitions between SI and HCCI were largely transparent and far smoother than any of the current production hybrids when starting and stopping the engine. Performance felt pretty much the same as a regular Vectra or Aura. The only detectable difference was a slight audible ticking when the engine was in HCCI. The technology definitely works; the main problem now will be making the control software robust enough to deal with all real world weather, road and driver conditions. XI. CONCLUSION HCCI has been identified as a 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 fuelrefining capability. Also, HCCI engines would probably cost less than CIDI engines because HCCI engines would likely use lower-pressure fuelinjection 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. In addition, for heavy-duty vehicles, successful development of the diesel-fueled HCCI engine is an important alternative strategy in the event that CIDI engines cannot achieve future NOx and PM emissions standards. HCCI engines will be cheaper than presently used engines because of their simplified construction. Currently, the only problem to be solved in future work is the balance improvement between load control strategies and HCCI engine exhaust gas emissions. REFERENCE [1] J.Hiltner, R. Agama, F. Mauss, B. Johansson, M. Christensen, Homogeneous charge combustion ignition operation with natural gas, ASME, Journal of engineering for gas turbine and power, 2003, Vol 125. [2] Chia-jui Chiang and Anna G.Stefanopoulou, Stability analysis in homogeneous charge compression ignition (HCCI) engines with high dilution IEEE Transactions on control systems Technology,Vol 12, Issue [3] Anders widd, Kent Ekholm, per Tunestal, Rolf Johansson, Physics Based model predictive Control of HCCI Combustion phasing using Fast Thermal Management and VVA, IEEE Transactions on control systems Technology,2012, Vol.20, Issue.3. [4] Nikhil Ravi, Mathew J. Rolle, Hsien-Hsin Liao, Adams F. Jungkunz, Chen-Fang, model-based Control on HCCI Engines using Exhaust recompression, IEEE Transactions on Control Systems Technology, Vol.18, issue.6,2010. IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 166