International Journal of Computer Engineering and Applications, Volume XII, Special Issue, March 18, ISSN

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1 International Journal of Computer Engineering and Applications, Volume XII, Special Issue, March 18, ISSN A REVIEW ON HOMOGENEOUS CHARGE COMPRESSION IGNITION ENGINE FOR ELIMINATION OF LIMITATIONS Vyom Bhushan Student, M.Tech Automobile Engineering, R.I.T. Islampur, India bhushanvyom21@gmail.com Dr. Sanjay D. Yadav Professor Automobile Engineering, R.I.T. Islampur, India sanjay.yadav@ritindia.edu Abstract In HCCI combustion, combustible mixture is made homogeneous in nature by premixing the charge and compressing it until the auto-ignition temperature is reached. The main characteristic of HCCI defines clearly that the ignition takes place at several places at a time and fuel/air mixture burns almost together. Due to indirect combustion ignition, the process of controlling the ignition becomes a difficult task. The HCCI engines can be beneficial economically and environmentally for the automobiles, as it releases low amount of NOx and consumes very less fuel. The controlling of temperature of combustion chamber and controlling of composition of mixture are the two difficult tasks in HCCI engine. The reduction of NOx and the improvements in efficiency by using double fuel HCCI combustion of natural gasgasoline mixtures has been studied. Scope for Research and Development in HCCI Engine like Combustion Phasing Control, Operational Range High load working has been discussed. The HCCI engines can be beneficial economically and environmentally for the automobiles, as it releases low amount of NOx and consumes very less fuel. Further research can be done to enhance HCCI Engine Combustion. Keywords hcci; combustion; emissions; engine; fuel I. INTRODUCTION The homogeneous charge compression ignition uses both types of combustion which are used in IC engines. Homogeneous charge spark ignition is used in gasoline engines and stratified charge compression ignition is used in diesel engines. Instead of producing an electric discharge for ignition of the mixture, the oxidizer and fuel are mixed together in homogeneous charge spark ignition and by compressing the mixture, its concentration and temperature are increased together until the complete ignition of whole mixture takes place. In same way, stratified charge compression ignition occurs during injection event and combustion takes place at the boundary of fuel/air mixture by increasing the temperature and concentration of the mixture through compression. The main characteristic of HCCI defines clearly that the ignition takes place at several places at a time 1

2 A REVIEW ON HOMOGENEOUS CHARGE COMPRESSION IGNITION ENGINE FOR ELIMINATION OF LIMITATIONS and fuel/air mixture burns almost together. Due to indirect combustion ignition, the process of controlling the ignition becomes a difficult task. HCCI can be controlled to have the emission as of gasoline engine and efficiency as of diesel engine. HCCI engines without after treatment catalytic converter show low level of NOx emissions but CO and HC emissions are high even now, because of lower peak temperature. Today's automotive engine manufacturers have also been started focusing on HCCI engines due to the ability of HCCI engine showing high efficiency of diesel engine and low NOx and particulate emissions. Regarding HCCI engines, researchers have to find solution to certain technical difficulties like combustion stability by rapid transients and control of ignition timing to reduce unburnt HC and CO emissions and operation at higher loads. In operation of HCCI engines, many different fuels are used. It is obvious in near future use of HCCI in automotive engines will have mix-mode combustion. In HCCI engines, low, medium and even high loads can be used as standard combustion in SI engines. II. LITERATURE REVIEW In comparison to diesel injection or spark ignition, HCCI engines are much older. Actually, HCCI was in use before electronic spark ignition. Hot-bulb engine is one of the example used for mixing fuel with air having a hot vaporization chamber. Extra heat promotes conditions for the occurrence of combustion. HCCI engines are better as they provide high efficiency and low emissions. Due to compression, the auto-ignition and burning of premixed lean charge takes place in HCCI engine. The dilution of charge is done by two ways, either by mixing the charge with exhaust gases which are recycled or by making the charge of very lean nature. Before implementation of HCCI in the production of engines, many technical difficulties have to be solved. SCCI is another variant of HCCI which has the capability to solve the difficulties of HCCI as it stratifies the charge and temperature. The engines are designed to provide a versatile facility for investigations of a wide range of several fuel-injection systems and the working situations, mixing of charge and residual gases and the controlling methods that have the ability to solve the difficulties of HCCI. The determination of engine size has been done by considering both areas of application of HCCI in automotive sector as well as in heavy duty industrial use. These engines were equipped with the following characteristics: Variable in-cylinder swirl Multiple fuel systems like fully premixed injection, port fuel injection, gasoline-type direct-injection, and diesel-type directinjection. Complete intake charge conditioning through simulated or real EGR, intake pressure up to 6 atm, intake temperature up to 220 C and speed up to 3600 rpm for a metal engine and 1800 rpm for an optical engine. Variable compression ratio through interchangeable pistons having compression ratio ranging from 12:1 to 21:1. The conversion of mechanical valves to variable valve actuation (VVA) is under development which further includes the charge stratification in order to improve the engine emissions and combustion efficiency during part load operation. The type of fuelaffects the performance and emissions of HCCI engine over a series of speeds and loads boosting for increased power, the effects of heat transfer, control of combustion phasing and extending operation to higher loads. The reduction in NOx and enhancement in efficiency of HCCI engine was experimentally tested by Pipitone and Genchi [1] using double fuel combustion of natural gas-gasoline mixtures on CFR engine provided with two injection systems for controlling the fuel mixture composition and air to fuel ratio. 23% increment of the engine efficiency was noticed and an effective reduction in pollutant emissions was found as compared to SI operation. Bahng et al. [2] predicted a new technology to overcome the limitation of delayed heat rate in spite of fast reaction of homogeneous charged state of HCCI engine with excess air through fuel modification. They performed experimental tests and found that the drawbacks caused by lean burn in the HCCI engine can be overcome easily. The effects of residual gas fraction (RGF) were investigatedexperimentally on homogeneous charged compression ignition (HCCI) combustion by Can et al. [3] and the experiments were performed at several values of lambda and by making intake air temperature constant at 80 C using Primary Reference Fuel with the blend of n-heptane (20%) and isooctane (80%) as the test fuel. [3] It was noticed that the phasing of combustion in HCCI engine can be controlled by using the cams having low lift and the combustion in HCCI can be stabilized by trapping exhaust gases which results in avoiding the phenomenon of knocking particularly at high engine loads. Dong et al. [4] developed a skeletal gasoline flame ionization mechanism with 62 species and 189 2

3 International Journal of Computer Engineering and Applications, Volume XII, Special Issue, March 18, ISSN reactions for predicting the ion current signal on HCCI engines. The PRF (Primary Reference Fuel), blends of iso-octane and n-heptane, was widely used for the research on gasoline-fueled HCCI engines. Also, they modeled HCCI engine with mechanism for gasoline, and flame ionization mechanism, containing 248 species and 1233 reactions. Mathivanan et al. [5] studied diesel injected in 5 timed pulses in a CI engine which was operated in homogeneous charge compression ignition mode. It was found that MP injection was superior than fuel injection in SP. Multiple pulse gives lesser emissions and high thermal efficiency due to its improved phasing of combustion and increased heat release rate. Chen et al. [6] analyzed variations in different cycles and the prior cycle effects of signals of ion current by evaluating against pressure transducer signals by applying the methods of time-series in an HCCI engine and also tested the effects of several calibrated ion signal intensities by adding cesium acetate (CsOAc) to the base fuel. Gowthaman and Sathiyagnanam [7] investigated the effect of both inlet air temperature and fuel injection pressure on performance and emission behaviour of homogeneous charge compression ignition engine (HCCI) fuelled with diesel fuel. The variation in inlet air temperature was done in between 40 C and 70 C and the variation in injection pressure was taken from 3 bar to 5 bar. [7] The optimum inlet air temperature and fuel injection were observed from the results. These results showed that the heating inlet air for improvement of diesel fuel vaporisation and the increment in inlet air temperature limited the operating range of HCCI engine, because of the high knocking intensity, high NOx emissions and the charge misfiring. Because of high level of HC and NOx emissions, fuel injection pressure was also limited. Ramesh and Mallikarjuna [8] evaluated in-cylinder mixture homogeneity in a diesel HCCI engine by CFD analysis. Global and local in-cylinder fuel distribution and in-cylinder fuel distribution index are used to evaluate the mixture homogeneity. Bissoli et al. [9] introduces a new foretelling multizone model which illustrates the homogeneous charge compression ignition combustion. The complicated chemistry engaged in the auto-ignition and the formation processes of the pollutants were examined by using kinetic mechanisms, RoPA and SA. Yang et al. [10] proposed fundamental HCCI engine experiments as a means for characterizing the impact ofmodern spark ignition technologies on the knock propensity of different fuels. Generally, the investigation hasbeen carried out by using ethanol on gasoline to demonstrate the impacts of turbocharging, downspeeding anddirect injection. They presented examples where HCCI experiments are used to identify biofuel compounds withgood potential for modern SI engine applications. III. WORKING OF HCCI ENGINE A. General Working of HCCI Engine In an HCCI engine, the control of fuel delivery plays an important role in controlling the combustion process. Firstly, during intake stroke, the fuel is injected into combustion chamber of each cylinder via fuel injectors which are mounted on the cylinder head. This is done by air induction which is produced during intake stroke. Fuel and air are mixed together in the combustion chamber of the cylinder at the end of intake stroke. Fig.1. Combustion in Gasoline, Diesel and HCCI Engine [11] Heat generation is started in combustion chamber when the piston starts to go up during compression stroke. By the end of this stroke, the amount of heat necessary to burn the charge is produced causing combustion of the fuel and air mixture, which forces the piston down. As the combustion process is lean as compared to spark ignition engines and compression ignition engines, there is low temperature and flameless energy available in the entire combustion chamber. The power is generated as a result of burning of entire homogeneous fuel mixture. When the power stroke comes to an end, the piston starts moving in reverse direction and it again initiates the exhaust stroke. The exhaust valves close before evacuating the whole exhaust gases, causing trapping of the latent heat of combustion. The fuel is injected in a little amount in to the combustion chamber earlier to the start of next intake stroke. 3

4 A REVIEW ON HOMOGENEOUS CHARGE COMPRESSION IGNITION ENGINE FOR ELIMINATION OF LIMITATIONS B. Theory of Controlling HCCI Combustion In HCCI combustion, no sharp edges were found in the intensity histogram of Planar Laser-Induced Fluorescence(PLIF) images, which represent the gradual process of transition from fuel to product as per the experimentation on the engine having high compression ratio, propagation of auto-ignition flame front was analyzed. The spreading of hot spots (auto-ignition regions of high temperature) to the surrounding colder gases has been investigated by mathematical analysis. It is found that auto-ignition flame front propagates into the unburnt fuel/air mixture at acoustic speed leading to producing detonation at a lower speed, higher than that of flame propagation which either leads to autoignitive deflagration or thermal processes. Very low temperature gradients are required for thermal explosion while medium temperatures are required for detonation whereas high temperature gradients are required for deflagration. C. Working Procedure Fuel is injected through fuel injectors. Air induction through intake plenum. Air & Fuel are mixed in combustion chamber. As piston moves back up (compression stroke), sufficient heat has accumulated. This heat (no spark) spontaneously combust A/F mixture which forces piston down for power stroke. Then lean, low temperature flame-less energy is released. Entire mixture burned simultaneously, produces equivalent power using much less fuel and low emissions. At exhaust stroke, exhaust valves closes early, trapping some latent combustion heat and preserved. Now, small amount of fuel injected in chamber for pre-charging before next stroke. IV. FUELS USED IN HCCI ENGINE Gasoline: Gasoline is obtained from petroleum and used n SI engines. It is a flammable liquid and volatile hydrocarbon mixture. Diesel: Diesel, a component obtained by distillation of crude oil, is a hydrocarbon mixture used as fuel. Ethanol:Ethanol is a supplement to gasoline. To reduce the cost, it is tried to be made from other low value feedstocks. Therefore, it is a renewable source of energy which contributes nothing to global warming. 85% ethanol and 15% unleaded gasoline are blended and named as E85 which is used as an alternative vehicle fuel. Also when gasoline is blended with 10% of ethanol, it oxidizes the gasoline and make it superb for most of the modern gasoline vehicles. Methanol: Methanol is an alternative fuel made from natural gas, the plant fibre of wood or coal and used as a supplement to gasoline. It can also be made from biomass through fermentation. Most of the methanol fuel is available as gasoline with 55% methanol. Alcohol fuels like M55 are almost as transparent as gasoline, distinction between the two is not easy. Natural Gas: CNG is the name given to compressed natural gas. There are two forms of natural gas which are used as a fuel in vehicles. These two forms are CNG and liquefied petroleum gas i.e., LPG. CNG kits are commonly available for the supply of fuels in cars. CNG fuel is cheap in comparison to petrol. Propane and Butane: Propane as well as butane are obtained from the wells of oil and gas. Both of these are refined by the petroleum refining process. The LPG is used in both types propane and butane are used in automobiles either individually or combination of both. LPG is the by product of crude oil and refined gas and it also has hydrocarbons in the form of vapours at NTP and converts into liquid at moderate pressure which mainly consists of propane. Hydrogen: Hydrogen is not found freely but obtained either by reforming natural gas or by splitting the water into oxygen and hydrogen through electrolysis of water. When the hydrogen used in an IC engine it only produces some traces of NOx nothing else. As there no carbon content present in hydrogen, so after burning of hydrogen, there is no generation of any green house gas. In comparison to battery, hydrogen can be filled in a in a hydrogen tank in a very less time means that the recharging time of battery is very short. Hydrogen is the best alternative fuel for long drives. Biodiesel: Biodiesel is one of the alternative fuel which has been made for using particularly in the present diesel engines. It is generally made from plant oils and the fat of animals by applying many chemical reactions. The biodiesel is non toxic in nature as well as renewable. In general, it is blended with the standard diesel fuel and B20 having 20% biodiesel and 80% standard diesel fuel. The B20 biodiesel is the most used biodiesel in automotive engines. Primary Reference Fuel - Blend of 20% n-heptane and 80% iso-octane (PRF80): The blend of 20% n- heptane and 80% isooctane (PRF80) was used as the test fuel and all the experiments were conducted at wide open throttle. Natural Gas Gasoline Mixtures, Double Fuel HCCI Combustion: The Bi-fuel engines having 4

5 International Journal of Computer Engineering and Applications, Volume XII, Special Issue, March 18, ISSN double injection are used in some modern vehicles which have another mode of combustion known as double fuel combustion which differs from the existing dual fuel combustion. As in double fuel combustion, one of the two fuels behaves as an igniter to propagate the flame of the other fuel. V. LIMITATIONS IN HCCI ENGINE The combustion control is the major difficulty in HCCI engine. The combustion timing is an easy task in case of SI engines just by changing the event of spark and the delivery of fuel by using EM control while in case of HCCI engines, the controlling of temperature of combustion chamber is a difficult task as the temperature changes so quickly and controlling of composition of mixture is also much difficult, as it has narrow thresholds like the load on engine, position of throttle and the pressure inside cylinder. Combustion Phasing Control Emission: HC and CO Homogenous Charge Preparation Limited Operating Range Abnormal Pressure Rise with Noise Cold Start Combustion Phasing Control One of the main challenge in HCCI engine is controlling the ignition timing which has effect on the power and efficiency. The conventional engines have direct mechanisms to control the start of combustion but HCCI engine lacks in such kind of mechanism. Combustion in SI engine is controlled by spark plug and CI engine by fuel injector. In HCCI engine, the start of combustion depends on the auto-ignition. Fig. 2. Single Fuel Injection Timing on Combustion Phasing [13] The combustion phasing in HCCI engines is influenced by the several factors like auto-ignition properties of the fuel, fuel concentration, residual rate, reactivity of the residual, mixture homogeneity, compression ratio, intake temperature, latent heat of vaporization, engine temperature, heat transfer to the engine and other engine dependent parameters. Combustion timing control is strongly desirable because if combustion occurs early then efficiency is affected with engine damage and if combustion occurs late, the chances of misfire increases. Several potential control methods have been proposed to control HCCI combustion: a. Varying the amount of exhaust gas recirculation (EGR) b. Using a variable compression ratio (VCR) c. Using variable valve timing (VVT) to change the effective compression ratio. d. The amount of hot exhaust gases retained in the cylinder. VCR and VVT technologies are particularly being under consideration as their time response could be made sufficiently fast to handle rapid transients (i.e., accelerations/ decelerations). High Levels of Emission: UHC and CO To improve the efficiency of combustion the exhaust should have low levels of UHC emissions. The UHC in the HCCI engine is mainly due to the incomplete oxidation of fuel. Some other reasons are crevice volumes present in the combustion chamber, valve overlapping, wall deposit absorption etc. The exhaust temperature is too low to oxidize UHC and CO to CO 2 and H 2O completely even during exhaust stroke. Due to low temperature combustion process, catalytic convertors are also inefficient to oxidize this pollutants. The efficiency of HCCI combustion is greatly improved by complete oxidation of fuel lastly by power stroke. The control of HC and CO emissions from HCCI engines will require exhaust emission control devices. Catalyst technology for HC and CO removal is well developed and has been standard equipment on automobiles for many years. However, the cooler temperatures of exhaust in HCCI engines may increase catalyst light-off time and decrease average effectiveness. As a result, to meet the future emission norms for HC and CO will likely require further development of oxidation catalysts for low-temperature exhaust streams. Chemical reduction of NOx and PM emission control devices are not so easy while HC and CO emission control devices are durable and simpler and their chemical oxidation is easy in HCCI engine. The HCCI engine has cold start problem. The compressed charge losses heat to the cold 5

6 A REVIEW ON HOMOGENEOUS CHARGE COMPRESSION IGNITION ENGINE FOR ELIMINATION OF LIMITATIONS combustion chamber walls at cold start operation. This problem can be sorted by starting the engine in the conventional mode for short warm-up period and then switch it to HCCI mode. There is need to develop new concepts to overcome the challenge of ignition in cold HCCI engines without compromising the warm engine performance. Most of the past researches are focussed on warm engine HCCI operation and less efforts have been made on the issue of cold start. There are some mechanisms which have been suggested for cold starting in HCCI mode. These mechanisms include glow plug, increase of compression ratio by the use of VCR and use of different fuels. To start the engine in spark ignition mode and transition to HCCI mode after warming may be considered as the practical approach. Homogenous Charge Preparation The mixture preparation is the key to achieve high economy and low emissions from the engine. The degree of homogeneity of the air-fuel mixture is greatly improved only by increasing mixture preparation time. Some other benefits of effective mixture preparation are control of wall wetting and oil dilution. Limited Operating Range Limited operating range is another challenge as compared to SI and CI combustion. This is influenced by several factors like engine geometry, fuel properties and auto-ignition process. Current research is carried out on light load operation which is also limited and still there is a lot to be carried out on high load operation. This is achieved by dual mode operation. It has been found that HCCI engines work well from low to medium loads but the difficulties have been encountered at high loads. The levels of NOx emissions and noise are unacceptable due to intense and rapid combustion. If the charge at high loads is partially stratified to stretch out the heat released event then operating range is remarkably increased. There are many mechanisms of stratification of partial charge. These mechanisms are injecting water, varying in-cylinder fuel injection and varying heat transfer by altering cylinder flows. The limit of extending the operating range by various techniques is not known at present and the development of the potential solution by R&D is awaited for future. Abnormal Pressure Rise with Noise In HCCI, due to simultaneous auto-ignition of the homogeneous charge during the compression stroke, the heat release is instantaneous which results in sudden rise in temperature followed by abrupt rise in the pressure leading to high levels of noise. Fig. 4. Individual Effects of Isothermal EGR on the Maximum Rate of Pressure Rise [13] Furthermore, at higher loads the rate of pressure rise can be so high that it may increase the engine noise considerably. If this condition is allowed to continue, then it may cause severe damage to the engine. Cold Start The HCCI ignition is very sensitive to the intake charge temperature and the small variations change the combustion phasing considerably. Fig. 3. Constraints to the HCCI Operating Range [13] 6

7 International Journal of Computer Engineering and Applications, Volume XII, Special Issue, March 18, ISSN Gasoline flame ionization mechanism to develop a chemical kinetic model for prediction of combustion timing by ion production in gasoline HCCI engine. Multiple fuel injection strategies of a diesel fuelled HCCI engine. By comparing against pressure transducer signals using time-series methods, the cyclic variations and prior-cycle effects of ion current signals are analyzed. By adding Cesium Acetate (CsOAc) to the base fuel, testing the effects of variouscalibrated ion signal intensities. Fig. 5. Valve lift curves in HCCI and SI modes using Variable Cam Timing(VCT) and Cam Profile Switching (CPS) [13] Furthermore, the initial temperature required to obtain auto-ignition condition changes with fuel properties and the operating conditions. HCCI engine will face a major problem in firing during cold start operations, as the temperatures are very low and the heat transfer to the cold combustion chamber walls is high. This problem can be overcome by starting the engine in a conventional mode and then switching over to the HCCI mode after a short warm-up period. At cold start, the compressed-gas temperature in an HCCI engine will be reduced because the charge receives no preheating from intake manifold and the compressed charge is rapidly cooled by heat transferred to the cold combustion chamber walls. Without some compensating mechanism, the low compressed-charge temperatures could prevent an HCCI engine from firing. VI. METHODS OF ELIMINATION OF LIMITATIONS Several methods are used to eliminate the limitations of a homogeneous charge compression ignition engine for different problems occurring to the engine as follows: By controlling the combustion phasing and stabilizing the combustion in HCCI engine by trapping the residual exhaust gases. To overcome the difficulty of delayed heating rate through the modification of fuel by vapourization of liquid gasoline with water electrolysis gas and air. By widening the range of possible operating conditions toenhance the performance ofdouble fuel HCCI combustion in a homogeneous charge compression ignition engine. VII. CONCLUSION HCCI is one of the recent trend in automotive engines in today's world. In HCCI combustion, combustible mixture is made homogeneous in nature by premixing the charge and compressing it until the auto-ignition temperature is reached. In the present work, the limitations and the methods of elimination of limitations have been discussed to improve HCCI engine for the further efforts to be made for replacing the current automotive combustion ignition technologies with it.the HCCI engines can bebeneficialeconomically and environmentally for the automobiles, as it releases low amount of NOx and consumes very less fuel. In future, these engines may be developed which can work even in high loads. There are many developments in HCCI engine with much scope for research and development. Further research can be done to enhance HCCI engine combustion. REFERENCES [1] Pipitone, Emiliano, Genchi, Giuseppe, "NOx reduction and efficiency improvements by means of the Double Fuel HCCI combustion of natural gas-gasoline mixtures", Applied Thermal Engineering, 102, pp , [2] Bahng, GunWoong, Jang, Dongsoon, Kim, Youngtae, Shin, Misoo, "A new technology to overcome the limits of HCCI engine through fuel modification", Applied Thermal Engineering, 98, pp , [3] Cınar, Can, Uyumaz, Ahmet, Polat, Seyfi, Yılmaz, Emre, Can, Ozer, Solmaz, Hamit, "Combustion and performance characteristics of an HCCI engine utilizing trapped residual gas via reduced valve lift", Applied Thermal Engineering, 100, pp , [4] Dong, Guangyu, Chen, Yulin, Li, Liguang, Wu, Zhijun, Dibble, Robert, "A skeletal gasoline flame ionization mechanism for combustion timing prediction on HCCI engines", Proceedings of the Combustion Institute, 000, pp. 1-8,

8 A REVIEW ON HOMOGENEOUS CHARGE COMPRESSION IGNITION ENGINE FOR ELIMINATION OF LIMITATIONS [5] Mathivanan, K., Mallikarjuna, J. M., Ramesh, A., "Influence of multiple fuel injection strategies on performance and combustion characteristics of a diesel fuelled HCCI engine - An experimental investigation", Experimental Thermal and Fluid Science, 77, pp , [6] Chen, Yulin, Dong, Guangyu, Mack, J. Hunter, Butt, Ryan H., Chen, Jyh-Yuan, Dibble, Robert W., "Cyclic variations and prior-cycle effects of ion current sensing in an HCCI engine: A time-series analysis", Applied Energy, 168, pp , [7] Gowthaman, S., Sathiyagnanam, A. P., "Effects of charge temperature and fuel injection pressure on HCCI engine", Alexandria Engineering Journal, 55, pp , [8] Ramesh, N., Mallikarjuna, J. M., "Evaluation of incylinder mixture homogeneity in a diesel HCCI engine - A CFD analysis", Engineering Science and Technology, an International Journal, 19, pp , [9] Bissoli, M., Frassoldati, A., Cuoci, A., Ranzi, E., Mehl, M., Faravelli, T., "A new predictive multi-zone model for HCCI engine combustion", Applied Energy, 178, pp , [10] Yang, Yi, Dec, John E., Sjӧberg, Magnus, Ji, Chunsheng, "Understanding fuel anti-knock performances in modern SI engines using fundaental HCCI experiments", Combustion and Flame, 162, pp , [11] [12] Dahl, Daniel, "Gasoline Engine HCCI Combustion Extending the high load limit", Thesis for the Degree of Doctor of Philosophy in Thermo and Fluid Dynamics, Department of Applied Mechanics, Chalmers University of Technology, Sweden, pp. 44, [13] Zhao, Hua, "HCCI and CAI engines for the automotive industry", Woodhead Publishing Limited and CRC Press LLC, Cambridge England,