Homogeneous Charge Compression Ignition Research Articles

Nonlinear feedforward controller design for air-path system with transport dynamics of external EGR system

Abstract Advanced combustion, such as homogenous charge compression ignition (HCCI), requires precise control of the in-cylinder gas condition. Such advanced combustion does not always result in stoichiometric combustion; therefore, the changes in the oxygen concentration of the burned gas must be considered in the controller design. Furthermore, the changes in the oxygen concentration in the exhaust manifold are transferred to the intake manifold with delay. In this research, the transport dynamics of the exhaust gas recirculation (EGR) path were modeled by a pure time-varying delay and a second-order filter, and the model was used to estimate the oxygen concentration through the EGR valve. The feedforward controller was obtained based on the inverse model, which calculates the throttle and EGR valve positions based on the target values of the intake manifold pressure, EGR ratio, and estimated oxygen concentration at the EGR valve. The control performance of the proposed feedforward controller was evaluated by conducting simulations using both the mean value model and the precise model constructed using 1D simulation software.

Effects of five different parameters on biodiesel HCCI combustion in free-piston engine generator

A coupled 3-D CFD and detailed chemical kinetics model of free-piston engine generator (FPEG) was adopted to investigate the effects of initial parameters on homogeneous charge compression ignition (HCCI) combustion and emission. Biodiesel with 115 species skeletal mechanism was selected as fuel. Five different parameters, namely the initial pressure, the initial temperature, the working frequency, the compression ratio and the fuel equivalence ratio, were selected to analyze their influences in the HCCI combustion simulation of FPEG. The simulation results showed that the change of the five parameters had visible impact on the heat release rate of HCCI combustion, which caused the in-cylinder temperature and pressure to change, and also caused the emission content of NOx and SOOT to change obviously.

Homogeneous Charge Compression Ignition (HCCI) Combustion: Combustion Process and Control Strategies

Homogeneous Charge Compression Ignition (HCCI), a low temperature combustion technology, is believed to be a promising technology due to low NOx and PM emissions and better fuel economy. HCCI combustion can realize homogeneous charge preparation in the cylinder and promote combustion auto-ignites in multiple spots by cooperative control of fuel chemistry and boundary conditions, such as Intake temperature, pressure, mixture concentration and EGR, which can short the flame propagation distance and accelerate the ignition and combustion speed. HCCI combustion control technology can be divided into two categories: one is to change the air/fuel mixing characteristics; the other is to change the working and design parameters of the engine. This paper reviews the establishment, improvement and development of HCCI combustion indirect control technology through the experimental research results of researchers in recent years.

Performance and emission characteristics of a diesel engine operated on diverse modes using renewable and sustainable fuels derived from dairy scum and municipal solid waste

Abstract Continuous utilization of crude oil in a diesel engine produces detrimental environmental effects. Therefore use of renewable fuels can at least lower the emission levels because such fuels are recyclable, provide energy safety and significantly deal with social, economic and environment. It is well known that diesel engine have several benefits compared to counterpart petrol engine and produce greater smoke and nitric oxide (NOx) levels. As a result, in this current work an effort has been carried out lower both smoke and NOx emission levels. To achieve this, homogeneous charge compression ignition engine (HCCI) is a better option. The influence of producer gas and dairy scum oil methyl ester (DiSOME) on the thermal efficiency and emission character of a compression ignition engine under dual and HCCI mode has been investigated. The HCCI engine was operated at constant air temperature (80 °C) because DiSOME cannot be vaporized at atmospheric temperature. The obtained with DiSOME-producer gas operated dual fuel mode provided amplified thermal efficiency (BTE) and declined hydrocarbon (HC), carbon monoxide (CO) and marginally augmented smoke and NOx levels compared to HCCI operation.

Performance analysis of HCCI and PCCI engines using computational fluid dynamics

In the current study, a numerical simulation for a three dimensional model of internal combustion (IC) engine consists of inlet valve, exhaust valve, inlet manifold and exhaust manifold, was carried out to analyse the HCCI and PCCI strategies using ANSYS 16.2. The computational fluid dynamics (CFD) analysis was carried out for different swirl numbers and essentially moderate values of the engine speed. The converged results of both the combustion strategies were compared for different wall adjacent temperature, mass average static pressure, apparent heat release rate and mass average turbulent kinetic energy. The outcome of simulations reflected that a PCCI combustion strategy is better than HCCI combustion strategy at lower rpm, while at the moderate and higher values of engine rpm, HCCI combustion strategy demonstrated better performance in terms of temperature, pressure and turbulent kinetic energy. Interestingly, the exergy destruction rate was observed higher in the case of homogeneous charge compression ignition combustion strategy.

Exergy loss characteristics of DME/air and ethanol/air mixtures with temperature and concentration fluctuations under HCCI/SCCI conditions: A DNS study

The exergy loss characteristics of combustion processes under homogeneous-charge compression ignition (HCCI) and stratified-charge compression ignition (SCCI) conditions are numerically investigated by analyzing two-dimensional (2-D) direct numerical simulation (DNS) data. Two fuels, dimethyl ether and ethanol, together with the initial conditions of different mean temperatures, and levels of temperature and concentration fluctuations relevant to HCCI/SCCI conditions were investigated. It is found that the prevalent deflagration mode significantly decreases the maximum exergy loss rates and spreads out the exergy loss rate for all the cases regardless of fuel types, temperature regimes, and temperature and/or concentration fluctuations. The primary irreversible sources of exergy loss are also identified. The chemical reaction is found to be the primary contributor to the total exergy loss, followed by heat conduction and mass diffusion, regardless of the fluctuation levels. It is also found that the relative change of exergy loss due to chemical reactions, ELchemrel, correlates strongly with the heat release fraction by deflagration. The maximum ELchemrel is found to be less than 10%. Chemical pathway analysis reveals that the exergy loss induced by low-temperature reactions, represented by the decomposition of hydroperoxy–alkylperoxy and the H-abstraction reactions of the fuel molecule, is much lower under the SCCI conditions than that under the HCCI conditions. Generally, the dominant reactions contributing to the exergy loss in the high-temperature regime are nearly identical for the HCCI and SCCI combustion. Key reactions, including the H2O2 loop reactions, the reactions of the H2–O2 mechanism, and the conversion reaction of CO to CO2, CO+OH=CO2+H, are found to contribute more than 50% of the total exergy loss. Due to locally higher reactivities by temperature and concentration fluctuations inducing deflagration dominance, these reactions occur at a relatively higher temperature (1600 K–1900 K) compared with the homogeneous zero-dimensional cases (∼1400 K), resulting in a net reduction in exergy loss.

Introduction of HCCI for Hydrogen Fuel Engines

This paper is a brief review of the homogeneous charge compression ignition (HCCI) model for hydrogen-fueled internal combustion engines based on an analysis of the advantages and disadvantages of hydrogen internal combustion engines and HCCI combustion. It found that HCCI can be realized in a hydrogen-fueled internal combustion engine, meanwhile the HCCI can effectively reduce the emission of hydrogen internal combustion engine.

Acoustic characterization of combustion chambers in reciprocating engines: An application for low knocking cycles recognition

In this paper the acoustic response of a combustion chamber is studied by assuming different pressure field excitation. The viscous effects on the combustion chamber and the finite impedance of the walls have been modeled with a first order system, which damps the resonance oscillation created by combustion. The characterization of the acoustic response of the combustion chamber has been used to identify the source of the excitation in order to distinguish normal combustion from knock. Two engines, a conventional spark ignited (SI) and a turbulent jet ignition (TJI) engine, were used, fueled with gasoline and compressed natural gas (CNG), respectively. The pressure fluctuations in the combustion chambers are analyzed and a pattern recognition system identifies the most likely source of excitation. This new criteria for knock identification permits a more consistent differentiation between knocking and no-knocking cycles, independent on the amplitude of the phenomenon, thus allowing the improvement for knock control algorithms, specially with combustion modes which heavily excite resonance, such as turbulent jet ignition or homogeneous charge compression ignition (HCCI).

Reduced Reaction Mechanisms for Ethanol under Ultra-lean Conditions in Internal Combustion Engines.

Chemical kinetics models for ethanol under ultra-lean engine conditions were evaluated to couple with CFD multidimensional simulations of a spark-assisted homogeneous charge compression ignition (HCCI) rotary engine. Five reduced reaction sets proper for CFD simulations and two detailed reaction mechanisms for comparison were tested by simulating ignition delay times, laminar flame speeds, and a single-cycle HCCI engine with virtual piston dimensions. The simulated results of the new mechanism with 188 reactions were well-fitted to both experimental ignition delay times for ultra-lean ethanol/air conditions and laminar flame speeds at high pressures. This reaction set resulted in better-simulated ignition delay times at 30 and 40 bar for ultra-lean ethanol/air conditions than other chemical kinetics models. Maximum temperatures and pressures of 2500–2580 K and 280–289 bar, respectively, were observed for hydrous ethanol/air under ultra-lean conditions in HCCI engine. In addition, the simulation results of the HCCI ethanol engine presented high pressure rise rates of 8–26 bar/CAD at 3600 rpm. These results indicated that the engine test should be carried out at 2500 rpm with 2 bar of boost pressure for CFD model calibration with the new optimized reaction mechanism.

PRELIMINARY STUDY OF WATER INJECTION ON THE COMBUSTION AND EMISSIONS CHARACTERISTICS IN A HCCI ETHANOL ENGINE

Our dependence on fossil fuels coupled with concerns about harmful emissions have motivated researchers to look for renewable fuels that have clean combustion and for advanced combustion modes. In this context, homogeneous charge compression ignition (HCCI) is an emerging technology which offers an alternative to conventional spark ignition and compression ignition engines and can operate on renewable fuels. Low temperature combustion, which can result in low NOx emissions with high indicated efficiency, is the more important characteristic of this combustion mode. It’s main problem is the combustion timing control due to lack of direct ignition control, once HCCI flame initiation is based on charge thermal state. Thus, controlled auto-ignition (CAI) combustion mode has been proposed. Several methods were proposed for combustion phasing control, between them, the injection of water in the intake manifold. This work investigated the influence of water injection in the intake runner of an ethanol HCCI cylinder from a converted three-cylinder diesel generator set, in which two cylinders operated on conventional diesel combustion and one diesel cylinder provided recycled exhaust gas for the one cylinder running on ethanol HCCI combustion. The water injection was used to control the CA50 combustion parameter. The results show that water injection is an efficient strategy to control the combustion timing, since the reactivity of the mixture can be controlled. The results at 400 and 600 kPa of IMEP and 1800 rpm indicated a good combustion stability, high efficiency and low emissions characteristics. The highest indicated fuel conversion efficiency found was 36.9% for 600 kPa of IMEP and 8 CAD of CA50. However, for 200 kPa of IMEP the combustion was unstable, the indicated efficiency was deteriorated and indicted CO emissions was high.

Detection of transient low-temperature combustion characteristics by ion current – The missing link for homogeneous charge compression ignition control?

Homogeneous charge compression ignition is a promising low-temperature combustion mode because of its high efficiency and low emissions; however, its strong cycle-to-cycle coupling effect, which caused by the recirculation of exhaust gases, may entail problems with low combustion stability. In this study, a new concept that extracts more comprehensive combustion information in homogeneous charge compression ignition is proposed through the integration of ion current and in-cylinder pressure sensing. To analyze the correlations of combustion parameters and their relationships with the ion current parameters, steady-state measurements were conducted. Dynamic measurements were implemented to form a comprehensive database for artificial neural network training. To investigate the hypothesis that the ion current gives additional information beyond the pressure trace, black-box models based on experimental data are trained. The results show that the baseline model trained purely with the manipulated variables has the worst performance, while the model including both in-cylinder pressure and ion current derived parameters has the best predictability, with the overall root-mean-square error reduced by 2.5% in predicting combustion phasing, compared with in-cylinder pressure based model. It demonstrates that a significant improvement in model quality can be achieved by the combination of ion current and in-cylinder pressure sensing, which indicates that the ion current signal contains information that goes beyond a sole analysis of the pressure trace. By complementing the in-cylinder pressure, the use of the ion current as a “chemical sensor” for low-temperature combustion thus appears very promising for the stable control of homogeneous charge compression ignition combustion.

A review of solid oxide fuel cell application

Solid oxide fuel cell (SOFC) is an efficient chemical fuel cell, which has been widely used in different fields. The successful application of this technology is of great significance to alleviate the energy crisis, meet the demand of the quantity and quality of electricity, and protect the ecological environment. SOFC has been utilized with gas turbine (GT), homogeneous charge compression ignition (HCCI) and small-scale power generation. This article introduces the characteristics, working principle and engineering application of solid oxide fuel cells in more detail.

Study the impact of fuel and exhaust gas recirculation on HCCI combustion

This paper presents a numerical study of fuel/fuel blends impact on rate of heat release at different exhaust gas recirculation rate in case of homogeneous charge compression ignition (HCCI) combustion. A direct injection engine is used for simulation which also allows mixture preparation in intake manifold leading to premixed combustion. The numerical analysis was conducted by means of an engine model developed in advanced simulation software AVL Boost. The combustion model is based on skeletal reaction mechanism of C7H16(n-heptane) that uses 26 species and 66 reactions. Additionally, to the main fuel, methane and hydrogen was added. Thus, the influence of fuel blends was evaluated at EGR rate within the range of 0% to 40%.

Analysis of ion current signal during negative valve overlap of HCCI combustion with high compression ratio

Homogenous charge compression ignition (HCCI) combustion is a low temperature combustion process which combines high combustion efficiency with ultra-low [Formula: see text] raw emissions. Steep increases of the in-cylinder pressure and unstable combustion sequences at the limits of the operating range can damage the engine and limit the use of HCCI to part load operation. This can be done using closed loop combustion control based on combustion parameters like the indicated mean effective pressure and the combustion phasing. Since in-cylinder pressure sensors are expensive components and therefore not suitable for series application, ion current sensors can be used as an additional source of information about the combustion. Combustion analysis using methods similar to those used in pressure based measurements can be implemented using an online analysis of the ion current signal. In this study, the ion current sensor will be examined for its suitability for combustion control under HCCI conditions with lean air/fuel ratios and high compression ratios. Research has found that the ion current signal is strongly depended on the boundary conditions. Especially the air/fuel ratio which plays an important role for signal strength during the combustion process. When using valve timings with negative valve overlap in combination with a fuel pre-injection, a further peak of the ion current signal close to the gas exchange top dead center can be found in addition to the one during combustion. At the same time, it is hard to extract information from the cylinder pressure signal during NVO. Under lean conditions this peak even exceeds the signal during combustion. This study analyzes the ion current signal during NVO and its potential to be used for future combustion control concepts. The ion current signal shows potential to stabilize HCCI combustion at high loads. However, the prediction of late combustion cycles is still challenging.

Effects of External Mixture Formation and EGR Technique on a Diesel-Fueled PCCI Engine

Limitations on exhaust emissions of diesel engines have become increasingly stringent due to increasing awareness of environmental protection. This challenges diesel engine manufacturers to find a new balance between engine performance and emissions. Advanced combustion modes for diesel engines, such as homogeneous charge compression ignition (HCCI) and premixed charge compression ignition (PCCI), which can simultaneously reduce exhaust emissions and substantially improve thermal efficiency, have drawn increasing attention. In order to allow enough time to prepare the homogeneous mixture, the external mixture formation technique was used to achieve PCCI combustion. A device known as diesel vaporizer was used to produce diesel vapors. Diesel vapors mix with air at intake port of an engine to form homogeneous charge before combustion starts. Exhaust gas recirculation technique was used to control early ignition of the premixed charge. It was observed from the experimentations that the use of external mixture formation technique with EGR in PCCI engine decreases the NOx emissions by 43.57% but increases HC and CO emissions due to low temperature combustion. The brake thermal efficiency obtained was just 1.9% less than the conventional CI engine.

On the Turbulence-Chemistry Interaction of an HCCI Combustion Engine

A numerical study was carried out to evaluate the influence of engine combustion chamber geometry and operating conditions on the performance and emissions of a homogeneous charge compression ignition (HCCI) engine. Combustion in an HCCI engine is a very complex phenomenon that is influenced by several factors that need to be controlled, such as gas temperature, heat transfer, turbulence and auto-ignition of the gas mixture. An eddy dissipation concept (EDC) combustion model was used to take into account the interaction between turbulence and chemistry. The model assumed that reactions occur in small turbulent structures called fine-scales, whose characteristic lengths and times depend mainly on the turbulence level. The model parameters were slightly modified with respect to the standard model proposed by Magnussen, to correctly simulate the characteristics of the HCCI combustion process. A reduced iso-octane chemical mechanism with 186 species and 914 chemical reactions was employed together with a sub-mechanism for NOx. The model was validated by comparing the results with available experimental data in terms of pressure and instantaneous heat release rate. Two engine chamber geometries with and without a cavity in the piston were considered, respectively. The two engines provided significant differences in terms of fluid-dynamic patterns and turbulence intensity levels in the combustion chamber. The results show that combustion started earlier and proceeded faster for the flat piston, leading to an increase in both the peak pressure and gross indicated mean effective pressure, as well as a reduction of CO and UHC emissions. An additional analysis was performed by considering a case without swirl for the flat-piston case. Such an analysis shows that the swirl motion reduces the time duration of combustion and slightly increases the gross indicated work per cycle.

A Numerical Study to Control the Combustion Performance of a Syngas-Fueled HCCI Engine at Medium and High Loads Using Different Piston Bowl Geometry and Exhaust Gas Recirculation

Abstract This study aims to analyze the effect of piston bowl geometry on the combustion and emission performance of the syngas-fueled homogenous charge compression ignition (HCCI) engine, which operates under lean air–fuel mixture conditions for power plant usage. Three different piston bowl geometries were used with a reduction of piston bowl depth and squish area ratio of the baseline piston bowl with the same compression ratio of 17.1. Additionally, exhaust gas recirculation (EGR) is used to control the maximum pressure rise rate (MPRR) of syngas-fueled HCCI engines. To simulate the combustion process at medium load (5 bar indicated mean effective pressure (IMEP)) and high loads of (8 and 10 bar IMEP), ansys forte cfd package was used, and the calculated results were compared with Aceves et al.’s Multi-zone HCCI model, using the same chemical kinetics set (Gri-Mech 3.0). All calculations were accomplished at maximum brake torque (MBT) conditions, by sweeping the air–fuel mixture temperature at the inlet valve close (TIVC). This study reveals that the TIVC of the air–fuel mixture and the heat loss rate through the wall are the main factors that influence combustion phasing by changing the piston bowl geometry. It also finds that although pistons B and C give high thermal efficiency, they cannot be used for the combustion process, due to the very high MPRR and NOx emissions. Even though the baseline piston shows high MPRR (23 bar/degree), it is reduced, and reveals an acceptable range of 10–12 bar/degree, using 30% EGR.

Engine efficiency enhancement and operation range extension by argon power cycle using natural gas

Argon power cycle engine has been proved as a promising technology to increase engine efficiency and to reduce engine out emissions. In this research work, experiments were conducted in a port injection single-cylinder engine with air and argon/oxygen as the working fluids under spark ignition, homogeneous charge compression ignition, and spark assisted compression ignition conditions. Natural gas was used as fuel. Experimental results indicate that argon power cycle increases thermal efficiency, extends lean burn limit, suppresses oxides of nitrogen and unburned hydrocarbon emissions, compared to conventional air cycle. The maximum thermal efficiency of argon power cycle reaches 41.5% under low equivalence ratios and high compression ratio conditions. Given a fixed oxygen content, the thermal efficiency increases with decreasing equivalence ratio until the lean burn limit. With the decrease of oxygen content from 21% to 7.5%, the thermal efficiency of argon power cycle first increases and then drops with the peak occurring at ~15%. In practical applications, the engine load of argon power cycle can be controlled by changing equivalence ratio, oxygen content, or both. With argon power cycle, the use of spark assisted compression ignition can further increase the combustion stability, thermal efficiency, and decrease unburned hydrocarbon emission. Combined with an optimal spark timing, the engine cycle’s coefficient of variation of the indicated mean effective pressure decreases up to 84% and the thermal efficiency increases up to 2%, compared to homogeneous charge compression ignition.

Performance of homogeneous charge compression ignition (HCCI) engine with common rail fuel injection

Homogeneous Charge Compression Ignition (HCCI) engine is a newly introduced technology. However, controlling the HCCI timing of ignition and theheat release rate, at all operating regimes, present the biggest challenge due to the complicated and highly coupled combustion problems. The successful implementation of the common rail injection system in diesel engines has made this possible. The main key for this success is the capability to optimize the most important fuel injection parameters, namely timing, rate, and duration.This work experimentally investigates the performance of an HCCI Diesel engine with a Common Rail Direct Injection (DI) fuel system. The engine used is a turbocharged 2776 cc, 4-stroke, 4-cylinder, water-cooled with overhead valve mechanism. The engine performance is evaluated and presented at different loads and speeds. The Apparent Heat Release Rate during combustion is evaluated from the measured cylinder pressure-crank angle data. The pressure in the fuel line is measured at the entry to different fuel injectors to investigate the effect of pressure wave propagation in the fuel line on the fuel injection system.

Development and Application of Ion Current/Cylinder Pressure Cooperative Combustion Diagnosis and Control System

The application of advanced technologies for engine efficiency improvement and emissions reduction also increase the occurrence possibility of abnormal combustions such as incomplete combustion, misfire, knock or pre-ignition. Novel promising combustion modes, which are basically dominated by chemical reaction kinetics show a major difficulty in combustion control. The challenge in precise combustion control is hard to overcome by the traditional engine map-based control method because it cannot monitor the combustion state of each cycle, hence, real-time cycle-resolved in-cylinder combustion diagnosis and control are required. In the past, cylinder pressure and ion current sensors, as the two most commonly used sensors for in-cylinder combustion diagnosis and control, have enjoyed a seemingly competitive relationship, so all related researches only use one of the sensors. However, these two sensors have their own unique features. In this study, the idea is to combine the information obtained from both sensors. At first, two kinds of ion current detection system are comprehensively introduced and compared at the hardware level and signal level. The most promising variant (the DC-Power ion current detection system) is selected for the subsequent experiments. Then, the concept of ion current/cylinder pressure cooperative combustion diagnosis and control system is illustrated and implemented on the engine prototyping control unit. One application case of employing this system for homogenous charge compression ignition abnormal combustion control and its stability improvement is introduced. The results show that a combination of ion current and cylinder pressure signals can provide richer and also necessary information for combustion control. Finally, ion current and cylinder pressure signals are employed as inputs of artificial neural network (ANN) models for combustion prediction. The results show that the combustion prediction performance is better when the inputs are a combination of both signals, instead of using only one of them. This offline analysis proves the feasibility of using an ANN-based model whose inputs are a combination of ion current and pressure signals for better prediction accuracy.