Strategies to Form Homogeneous Mixture and Methods to Control Auto-Ignition of HCCI Engine

2021 ◽  
Vol 18 (4) ◽  
Author(s):  
Ibham Veza ◽  
Mohd Farid Muhamad Said ◽  
Zulkarnain Abdul Latiff ◽  
Mohd Azman Abas ◽  
Mohd Rozi Mohd Perang ◽  
...  
Keyword(s):  
Pressure Rise ◽  
Homogeneous Mixture ◽  
Nox Formation ◽  
Operating Range ◽  
Hcci Engine ◽  
Hcci Combustion ◽  
Auto Ignition ◽  
Soot Emissions ◽  
Comprehensive Classification

Homogeneous charge compression ignition (HCCI) engine has emerged as a promising combustion technology. Theoretically, an HCCI engine can reduce both NOx and soot emissions significantly down to almost zero levels. This is possible as a result of two fundamental processes that occur in the HCCI engine, i.e. the homogeneous mixture and its autoignition characteristics. Neither spark plug nor injector is used in the HCCI engine. The autoignition of the homogeneous mixture is solely influenced by its chemical reactions inside the combustion chamber. However, this is where the problems start to occur. At low loads or too lean mixtures, misfire may occur, thus increasing the HC and CO emissions. At high loads or too rich mixtures, soot emissions and knocking tendency may increase. Moreover, an undesirable pressure rise due to knocking will increase the combustion temperature and potentially increase the probability of NOx formation. Therefore, the operating range of HCCI engine is very limited only to part loads. Controlling its combustion phasing play an important role to extend the narrow operating range of the HCCI engine. Despite numerous review articles have been published, classification of the approaches to achieve HCCI combustion in diesel engines were rarely presented clearly. Therefore, this review article aims to provide a concise and comprehensive classification of HCCI combustion so that the role and position of each strategy found in the literature could be understood distinctively. In short, two important questions must be solved to have successful HCCI combustion; (1) how to form a homogeneous mixture? and (2) how to control its auto-ignition?

Computational Analysis of an Early Direct Injected HCCI Engine with Turbocharger Using Bio Ethanol and Diesel Blends

2015 ◽  
Vol 812 ◽  
pp. 70-78
Author(s):  
S. Natarajan ◽  
A.U. Meeanakshi Sundareswaran ◽  
S. Arun Kumar ◽  
N.V. Mahalakshmi
Keyword(s):  
Chemical Kinetics ◽  
Computational Analysis ◽  
Reaction Path ◽  
Chemical Species ◽  
Operating Conditions ◽  
Injection Time ◽  
Engine Operation ◽  
Hcci Engine ◽  
Hcci Combustion ◽  
Auto Ignition

In this paper the work deals with the computational analysis of early direct injected HCCI engine with turbocharger using the CHEMKIN-PRO software. The computational analysis was carried out in the base of auto ignition chemistry by means of reduced chemical kinetics. For this study the neat diesel and Bio ethanol diesel blend (E20) were used as fuel. The inlet pressure was increased to 1.2 bar to simulate the turbocharged engine operation. The injection time was advanced to 18° before top dead centre (BTDC) i.e., 5° BTDC than normal injection time of 23° BTDC. The equivalence ratio was kept at 0.6 (ɸ=0.6) and the combustion, emission characteristics and chemical kinetics of the combustion reaction were studied. Since pressure and temperature profiles plays a very important role in reaction path at certain operating conditions, an attempt had been made here to present a complete reaction path investigation on the formation/destruction of chemical species at peak temperature and pressure conditions. The result showed that main draw backs of HCCI combustion like higher levels of unburned hydrocarbon emissions and carbon monoxide emissions are reduced in the turbocharged operation of the HCCI engine when compared to normal HCCI engine operation without turbocharger.

An Experimental Research on the Effects of Negative Valve Overlap on Performance and Operating Range in a Homogeneous Charge Compression Ignition Engine With RON40 and RON60 Fuels

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Seyfi Polat ◽  
Hamit Solmaz ◽  
Ahmet Uyumaz ◽  
Alper Calam ◽  
Emre Yılmaz ◽  
...  
Keyword(s):  
Pressure Rise ◽  
Engine Performance ◽  
Maximum Pressure ◽  
Compression Ignition ◽  
Compression Ignition Engine ◽  
Operating Range ◽  
Hcci Combustion ◽  
Residual Gas ◽  
Negative Valve Overlap ◽  
Valve Overlap

Abstract In this study, the effects of negative valve overlap (NVO) on homogenous charge compression ignition (HCCI) combustion and engine performance were experimentally investigated. A four stroke, single cylinder, port injection HCCI engine was operated at −16 deg crank angle (CA), −8 deg CA, and +8 deg CA valve overlap values and different lambda values and engine speeds at wide open throttle. RON40 and RON60 were used as test fuels in view of combustion and performance characteristics in HCCI mode. The variations of indicated mean effective pressure (IMEP), residual gas, CA50, indicated thermal efficiency (ITE), indicated specific fuel consumption (ISFC), maximum pressure rise rate (MPRR) and ringing intensity (RI) were observed on HCCI combustion. The results showed that NVO caused to trap residual gases in the combustion chamber. Hot residual gases showed heating and dilution effect on HCCI combustion. Combustion was retarded with the presence of residual gas at −16 deg CA NVO. Test results showed that higher imep and maximum in-cylinder pressure were obtained with RON60 according to RON40. As expected, CA50 was obtained later with RON60 compared to RON40 due to more resistance of auto-ignition. RON60 residual gas prevented the rapid and sudden combustion due to higher heat capacity of charge mixture. RI decreased with the usage of RON60 compared to RON40. Significant decrease was seen on RI with RON60 especially at lower lambda values. It was seen that HCCI combustion can be controlled with NVO and operating range of HCCI engines can be extended.

Application of Variable Valve Actuation Strategies and Direct Gasoline Injection Schemes to Reduce Combustion Harshness and Emissions of Boosted HCCI Engine

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Jacek Hunicz ◽  
Maciej Mikulski
Keyword(s):  
Pressure Rise ◽  
Operating Conditions ◽  
Exhaust Valve ◽  
Boost Pressure ◽  
Pressure Reduction ◽  
Intake Valve ◽  
Valve Timing ◽  
Hcci Engine ◽  
Auto Ignition ◽  
The Impact

The present study investigates various measures to reduce pressure rise rates (PRRs) in a residual-affected homogeneous charge compression ignition (HCCI) engine. At the same time, the impact of those measures on efficiency and emissions is assessed. Experimental research was performed on a single cylinder engine equipped with a fully flexible valve train mechanism and direct gasoline injection. The HCCI combustion mode with exhaust gas trapping was realized using negative valve overlap (NVO) and fuel reforming, achieved via the injection of a portion of fuel during exhaust recompression. Three measures are investigated for the PRR control under the same reference operating conditions, namely: (i) variable intake and exhaust valve timing, (ii) boost pressure adjustment, and (iii) split fuel injection to control the amount of fuel injected for reforming. Variable exhaust valve timing enabled control of the amount of trapped residuals, and thus of the compression temperature. The reduction in the amount of trapped residuals, at elevated engine load, delays auto-ignition, which results in a simultaneous reduction of pressure rise rates and nitrogen oxides emissions. The effects of intake valve timing are much more complex because they include the variability in the amount of intake air, the thermodynamic compression ratio, as well as the in-cylinder fluid flow. It was found, however, that both early and late intake valve openings (IVOs) delay auto-ignition and prolong combustion. Additionally, the reduction of the amount of fuel injected during exhaust recompression further delays combustion and reduces combustion rates. Intake pressure reduction has by far the largest effect on peak pressure reduction yet is connected with excessive NOX emissions. The research successfully identifies air-path and injection techniques, which allow for the control of combustion rates and emissions under elevated load regime.

Application of Variable Valve Actuation Strategies and Direct Gasoline Injection Schemes to Reduce Combustion Harshness and Emissions of Boosted HCCI Engine

2018 ◽  
Author(s):  
Jacek Hunicz ◽  
Maciej Mikulski
Keyword(s):  
Pressure Rise ◽  
Operating Conditions ◽  
Exhaust Valve ◽  
Boost Pressure ◽  
Pressure Reduction ◽  
Intake Valve ◽  
Valve Timing ◽  
Hcci Engine ◽  
Auto Ignition ◽  
The Impact

One of the pending issues regarding Homogeneous Charge Compression Ignition (HCCI) engines is high load operation limit constrained by excessive pressure rise rates (PRRs). The present study investigates various measures to reduce combustion harness in a residual-affected HCCI engine. At the same time, the impact of those measures on efficiency and emissions is assessed. Experimental research was performed on a single cylinder engine equipped with a fully-flexible valvetrain mechanism and direct gasoline injection. The HCCI combustion mode with exhaust gas trapping was realized using negative valve overlap and fuel reforming, achieved via the injection of a portion of fuel during exhaust re-compression. Three measures are investigated for the PRR control under the same reference operating conditions, namely: (i) variable intake and exhaust valve timing, (ii) boost pressure adjustment and (iii) split fuel injection to control the amount of fuel injected for reforming. Variable exhaust valve timing enabled control of the amount of trapped residuals, and thus of the compression temperature. The reduction in the amount of trapped residuals, at elevated engine load, delays auto-ignition, which results in a simultaneous reduction of pressure rise rates and nitrogen oxides emissions. The effects of intake valve timing are much more complex, because they include the variability in the amount of intake air, the thermodynamic compression ratio as well as the in-cylinder fluid flow. It was found, however, that both early and late intake valve openings delay auto-ignition and prolong combustion. Additionally, the reduction of the amount of fuel injected during exhaust re-compression further delays combustion and reduces combustion rates. Intake pressure reduction has by far the largest effect on peak pressure reduction yet is connected with excessive NOx emissions. The research successfully identifies air-path and injection techniques, which allow for the control of combustion rates and emissions under elevated load regime, thus shorting the gap towards the real-world application of HCCI concepts.

Numerical Exploration on HCCI Combustion Characteristics under NVO Strategy

2012 ◽  
Vol 614-615 ◽  
pp. 143-148
Author(s):  
Yin Han Gao ◽  
De Fu Wang ◽  
Peng Cheng ◽  
Hua Li ◽  
You Kun Wang
Keyword(s):  
High Efficiency ◽  
Combustion Characteristics ◽  
Oh Radical ◽  
3 Dimensional ◽  
Hcci Combustion ◽  
Auto Ignition ◽  
Early Closure ◽  
Soot Emissions ◽  
Negative Valve Overlap ◽  
No Emissions

Homogeneous charge compression ignition (HCCI) offers high efficiency and ultra-low NOx and SOOT emissions which raises world-wide attention. A 3-dimensional CFD HCCI model has been established using STAR-CD code for combustion characteristics studies under negative valve overlap (NVO) strategy via an early closure of exhaust valve. The combustion characteristics of HCCI were investigated. Simulation results were in good agreement with the available experimental data. Studies on in-cylinder temperature and OH radical concentration showed almost the same spatial distribution when auto-ignition occurred, OH radical had higher concentration in the field of higher temperature. The φ-T maps showed extraordinarily low NO emissions and no soot emissions under HCCI combustion. It was found that OH concentration rapidly increased after the start of the combustion at 356°CA and NO emissions were formed when the temperature was high enough at 358°CA. Most of CO emissions were converted to CO2 through the main combustion.

scholarly journals Effects of spark assist on HCCI combustion

2015 ◽  
Vol 161 (2) ◽  
pp. 73-77
Author(s):  
Jacek HUNICZ ◽  
Michał GĘCA ◽  
Paweł KORDOS ◽  
Alejandro MEDINA
Keyword(s):  
Flame Propagation ◽  
Pressure Rise ◽  
Spark Discharge ◽  
Combustion Stability ◽  
Experimental Heat ◽  
Hcci Combustion ◽  
Auto Ignition ◽  
Negative Valve Overlap ◽  
Compression Ignition Combustion ◽  
Valve Overlap

HCCI (homogeneous charge compression ignition) combustion is initiated by compression temperature and is independent of spark discharge. However, spark discharge can be applied under certain conditions to achieve hybrid combustion, where combustion by flame propagation is followed by auto-ignition of the unburned mixture. Spark assist can be applied to improve combustion stability at low loads or to reduce pressure rise rates under high load regime. In the current study variable spark ignition timing was applied for stoichiometric HCCI combustion, achieved using negative valve overlap technique. Under investigated conditions increase of nitrogen oxides emissions, due to flame propagation, was not observed. To provide more insight into combustion evolution, double Wiebe function was fitted to experimental heat release rates. It was found that only less than 10% of mixture was burned by flame propagation, even for very advanced spark discharge.

Effects of Intake Temperature on the Combustion Characteristics of HCCI Engine Fueled with n-Butanol

2014 ◽  
Vol 700 ◽  
pp. 651-654 ◽  
Author(s):  
Gang Li ◽  
Chun Hua Zhang ◽  
Ye Chong Shen ◽  
Ya Chong Shen ◽  
Jia Wang Zhou
Keyword(s):  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Pressure Rise ◽  
Combustion Characteristics ◽  
Combustion Stability ◽  
Maximum Heat ◽  
Hcci Engine ◽  
Hcci Combustion ◽  
P Rate

In order to study the influence of intake temperature on the combustion characteristics of HCCI engine fueled with n-butanol, the 2nd cylinder of a water-cooled, naturally aspirated and double-cylinders diesel engine was converted into HCCI combustion mode. The cylinder pressure (P), rate of pressure rise (dp/dφ), heat release rate (dQ/dφ) and cycle-to-cycle variations (CCV) were compared and analyzed by bench tests under the conditions with different intake temperatures at engine speed of 1000r/min, excess air coefficient of 2.5. The experiment results show that the peak pressure (Pmax), the peak rate of pressure rise and maximum heat release rate tend to rise and the peak arrives in advance with the increase of intake temperature. As the intake temperature rises, the coefficient of variation for Pmaxreduces and combustion stability increases.

scholarly journals UV Spectral Classification of B Stars

1985 ◽  
Vol 111 ◽  
pp. 411-413
Author(s):  
Janet Rountree ◽  
George Sonneborn ◽  
Robert J. Panek
Keyword(s):  
Classification System ◽  
Classification Criteria ◽  
High Dispersion ◽  
Spectral Classification ◽  
Early Type ◽  
B Stars ◽  
Dimensional Classification ◽  
Early Type Stars ◽  
Comprehensive Classification

Previous studies of ultraviolet spectral classification have been insufficient to establish a comprehensive classification system for ultraviolet spectra of early-type stars because of inadequate spectral resolution. We have initiated a new study of ultraviolet spectral classification of B stars using high-dispersion IUE archival data. High-dispersion SWP spectra of MK standards and other B stars are retrieved from the IUE archives and numerically degraded to a uniform resolution of 0.25 or 0.50 Å. The spectra (in the form of plots or photowrites) are then visually examined with the aim of setting up a two-dimensional classification matrix. We follow the method used to create the MK classification system for visual spectra. The purpose of this work is to examine the applicability of the MK system (and in particular, the set of standard stars) in the ultraviolet, and to establish classification criteria in this spectral region.

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