Modeling Direct-Injection Gasoline HCCI Combustion Using Detailed Chemistry and CFD

ABSTRACTAchieving the new emission norms is a difficult task to today’s compression ignition (CI) engine without any exhaust gas after-treatment technologies. It is necessary to find the practical method which reduces the unsafe emission, with minor modifications of the CI engine. Dual fuel homogeneous charge compression ignition (HCCI) engine has been recognised as one of the solutions to minimise the emissions and achieve higher performance. In the present study the dual fuel HCCI engine mode of operation carried out by supply of ethanol fuel-air mixture to the engine cylinder through the carburetor and diesel fuel is directly injected at the end of compression for the initiation of ignition. Dual fuel HCCI engine is one of the most promising engines suitable for alternative fuels and lower NOX emissions. An experimental investigation is carried out on dual fuel HCCI engine. Fuel consumption and exhaust emissions such as NOX, CO2, CO, HC are measured and compared with conventional CI engine. The results show that NOX emission tends to decrease at low and moderate loads of the engine, but at full load condition it is slightly higher. Further, thermal efficiency is calculated and compared in CI engine; it is observed that there is a slight improvement in thermal efficiency at high load operation. In the dual fuel HCCI engine mode, there is a provision to use of ethanol or any other alternate fuel for better energy efficiencies and low NOX emission.

The main aim of this study is to investigate theoretically the formation of nitric oxide (NO) in a homogeneous charge compression ignition (HCCI) engine fueled with blends of ethanol and synthetic gasoline (RON25, RON50, RON75). A detailed kinetic mechanism involving 1086 chemical species and 4754 elementary reactions taking place in a HCCI engine modeled as an adiabatic single-zone reactor was applied to simulate the emission of the investigated pollutant. A close agreement between experimental and calculated results of ignition delay, species concentrations in ideal reactors, and laminar flame velocities of pure ethanol, n-heptane and iso-octane confirmed the reliability of the kinetic model. An analogous comparison, but considering a set of data (NO formation, temperature, and pressure) obtained in a single-cylinder HCCI engine operated with different mixtures of primary reference fuels (n-heptane and iso-octane) over the equivalence ratio range from approximately 0.15 to 0.4, revealed the consistency of the adiabatic single-zone model. Despite the low to moderate content of NO typically observed in the exhausts from HCCI engines, a further decrease of this pollutant was still revealed at all the considered simulating conditions when the percentage of ethanol in the fuel (synthetic gasoline) was increased. However, the extent of NO reduction was more evident for blends involving up to approximately 20% of ethanol (<E20) and synthetic gasolines with low octane number (<RON50). From a practical point-of-view, this finding reveals that the injection of a small volume of ethanol to gasoline (<20%) could be an alternative procedure to reduce the rates of exhaust gas recirculation applied to control the HCCI operation, making it a promising strategy to have a conciliation between low NO and moderate UHC and CO emissions in gasoline HCCI.

&lt;div class="htmlview paragraph"&gt;A naturally aspirated in-line six-cylinder 2.9-litre Volvo engine is operated in Homogeneous Charge Compression Ignition (HCCI) mode, using camshafts with low lift and short duration generating negative valve overlap. This implementation requires only minor modifications of the standard SI engine and allows SI operation outside the operating range of HCCI. Standard port fuel injection is used and pistons and cylinder head are unchanged from the automotive application. A heat exchanger is utilized to heat or cool the intake air, not as a means of combustion control but in order to simulate realistic variations in ambient temperature. The combustion is monitored in real time using cylinder pressure sensors.&lt;/div&gt; &lt;div class="htmlview paragraph"&gt;HCCI through negative valve overlap is recognized as one of the possible implementation strategies of HCCI closest to production. However, for a practical application the intake temperature will vary both geographically and from time to time. It is therefore very important to gain knowledge of how this variation affects the combustion process.&lt;/div&gt; &lt;div class="htmlview paragraph"&gt;The operating range in HCCI mode for this specific engine stretches from 650 rpm to 4000 rpm and from 1 bar IMEP to 4 bar IMEP. The emissions of NO&lt;sub&gt;x&lt;/sub&gt; are approximately two orders of magnitude lower in HCCI mode compared to SI mode. The emissions of CO are slightly lower while the emissions of HC are slightly higher for HCCI operation. When run in HCCI mode the engine's efficiency is improved throughout the operating range by as much as 10 percentage units compared to SI operation. The effect of inlet air temperature variation on HCCI combustion through negative valve overlap is insignificant when the engine runs well inside of the HCCI operating range. The effect is however prominent when the engine is operated close to the border of the operating range.&lt;/div&gt;

The homogeneous charge compression ignition (HCCI) engine is a promising technology in terms of both soot and NOx emission. Natural gas (NG) is advantageous especially for HCCI engines with its single stage combustion, low C/H ratio, and high octane number. Since the main challenge of HCCI technology is stability and transient operations, using HCCI for constant speed operations may be advantageous. In this study, a CI diesel engine, which is used as a generator at constant speed, was modified and converted into an NG-fuelled, SI engine. Then, the engine was supplied with NG for SI, HCCI, and spark-assisted HCCI experiments. Spark-assisted operations were executed by using 3, 5, and 7 degree ignition advance values to assist HCCI combustion. In-cylinder pressure variations, exhaust temperature, specific fuel consumption, and emission values were investigated for comparison of different strategies. Experimental results showed that using the HCCI strategy and retardation of ignition advance of spark-assisted HCCI operations reduced maximum pressure. Therefore, these strategies improved NOx emissions, while HC emissions were slightly increased. The spark-assisted HCCI strategy improves the stability of operation while increasing CO emission. The specific fuel consumption value of HCCI was slightly higher than that of SI operation, while it was lower than spark-assisted strategies.

Different intake valve timings and fuel injection amount were tested in order to identify their effects on exhaust emissions and combustion characteristics using variable valve actuation (VVA) in a Homogeneous Charge Compression Ignition (HCCI) engine. HCCI engine is a promising concept for future automobile engines and stationary power plants. Two-stage ignition process in a HCCI engine creates advanced ignition and stratified combustion, this makes ignition timing and combustion rate controllable. Meanwhile, the periphery of fuel-rich zone leads to fierce burning, which results in slightly high NOx emissions. The experiments were conducted in a modified single cylinder water-cooled diesel engine. In this experiment we use diesel, bio-diesel (Jatropha) and gasoline as the fuel at different mixing ratios. HCCI has advantages in high thermal efficiency and low emissions and possibly become a promising combustion method in internal combustion engines.

Homogeneous Charge Compression Ignition (HCCI) combustion in a small-scale engine (25 cc) was experimentally examined. Historically, HCCI combustion has been studied in engines sized for passenger vehicles and trucks (approximately 500 cc and larger). HCCI combustion in large-scale engines is characterized by higher efficiency than SI and CI combustion. High rates of heat flux, due to large surface area to volume ratio and engine body material, initially prevented the small-scale engine from operating in HCCI mode. The high level of heat transfer was overcome and sustained small-scale HCCI operation was achieved with n-heptane fuel. Large-scale HCCI engines utilize ultralow equivalence ratios to achieve high efficiencies. The small-scale HCCI engine could not operate with equivalence ratios lower than 0.73. Performance characteristics including power, efficiency, and NOx emissions of the small-scale HCCI engine were poorer than when operated in SI mode. Recommendations to overcome high rates of heat flux and increase small-scale HCCI engine efficiency are presented.

Scientists are interested in a homogeneous charge compression ignition combustion model (HCCI) to replace a conventional combustion model on an internal combustion engine.This combustion model has the same performance as a direct-injection gasoline engine and the same type of ignition as a diesel engine.However, the NOx emission component is significantly reduced, while the smoke level is almost zero.With this combustion model, it's perfectly capable of meeting emissions requirements without having to be equipped with an additional emission after-treatment system.In this study, the author converted a traditional one-cylinder diesel engine into a new engine based on HCCI mode.In order to be able to work in HCCI mode, it is necessary to modify the engine's parameters, such as reducing the compression ratio, equipping it with a port fuel supply system, or combining air heating and exhaust recirculation systems.The study results have shown that the converted engine can operate according to the principle of HCCI in low load conditions of up to 30%.The combustion characteristics and engine operation parameters before and after conversion to HCCI mode are tested and evaluated on the engine test bed.Experimental research to quantify and assess the engine's HCCI operating mode and construct a set of control parameters for setting and widening the working regime in HCCI mode.

Evaluation of Homogeneous Charge Compression Ignition (HCCI) autoignition development through chemiluminescence imaging and Proper Orthogonal Decomposition

Emissions remain a critical issue affecting engine design and operation, while energy conservation is becoming increasingly important. One approach to favorably address these issues is to achieve homogeneous charge combustion at lower peak temperatures with a high compression ratio - the goal of Homogeneous Charge Compression Ignition (HCCI) engines. This thesis focuses on developing appropriate kinetic models for HCCI engines and on experimentally exploring new paths to address the limitations with current and advanced technologies. Since fuel oxidation chemistry determines HCCI engine performance, a model describing fuel oxidation at these conditions would be a useful design tool. HCCI engine experiments were conducted to provide the essential database for modeling, including temperature, pressure, ignition delay, and heat release. An existing pre-ignition skeletal chemical kinetic model was applied to HCCI ignition. Then, it was improved and extended to cover the entire HCCI combustion process. A global reaction model also was constructed for CFD simulations. Simulations using these models are generally in good agreement with the experimental data. During our investigations into HCCI and autoignition processes, we have observed some ignitions that begin at much lower temperature (&lt; 550 K) than expected. This is at odds with the generally accepted explanation of autoignition in HCCI engines, that the reactivity is driven by temperature, where autoignition occurs after the mixture has reached some critical temperature (approx. 1000 K). We have attempted to investigate the origins of these lower temperature autoignition phenomena, and we propose that traditional models may be missing the low temperature chemistry that explains this behavior. Our analysis indicates that proper utilization of these lower temperature phenomena may provide a means to better control SI, CI, and HCCI engines. Finally, to develop a better understanding of the autoignition chemistry of fuel mixtures and blends, this study investigated the preignition behavior of nheptane, iso-octane, and propionaldehyde blends in a pressurized flow reactor. Experimental results indicated that the effect of fuels in blends can be interpreted in terms of their radical scavenging behavior. To be effective as a scavenger, a fuel must have an overlapping reactivity range and a lower reactivity than the other fuel.

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;The carbon-neutral biodiesel is a promising renewable substitute for fossil diesel that renders the traditional oxides of nitrogen-particulate matter (NO&lt;sub&gt;x&lt;/sub&gt;-PM) trade-off into a unidirectional NO&lt;sub&gt;x&lt;/sub&gt; control problem. Low-temperature combustion (LTC) modes such as homogenous charge compression ignition (HCCI) are attractive for obtaining ultra-low NO&lt;sub&gt;x&lt;/sub&gt; and PM emissions. Studies on utilizing biodiesel fuel for HCCI combustion mode are sparsely available. Moreover, biodiesel emulsions in the HCCI combustion mode have not been attempted so far. Based on this premise, the present work explored the potential to utilize biodiesel and its emulsions having 20% and 25% water by volume under HCCI operating conditions. Biodiesel was prepared from a non-edible Karanja oil. The biodiesel emulsions were prepared using a heated magnetic stirrer apparatus with 3% by volume of the raw Karanja oil as a surfactant. A production light-duty diesel engine is modified to run in external mixture preparation based HCCI mode. An air-preheater and a fuel vaporizer aid in vaporizing the low volatile biodiesel injected into the inner surface of the vaporizer at 300 bar pressure using a common rail direct injection (CRDI) system. The engine compression ratio was fixed at 15, the maximum operable value with biodiesel. The results show that the engine could be operated only up to 20% of the rated load with biodiesel. With biodiesel-water emulsion, 30% of the rated load could be achieved. The maximum cylinder pressure was higher, and the heat release rate was advanced with emulsions compared to neat biodiesel. The brake specific fuel consumption was reduced by 35%, and the brake thermal efficiency increased by 2.4%, along with ultra-low NO&lt;sub&gt;x&lt;/sub&gt; and smoke emissions with emulsions. The present study shows the potential to utilize biodiesel-water emulsions in HCCI mode with reduced exhaust emissions. Suitable charge dilution methods must be adopted to extend the HCCI operating load range with emulsions.&lt;/div&gt;&lt;/div&gt;

Homogeneous charge compression ignition (HCCI) engine combines the combustion characteristics of a compression ignition engine and a spark ignition engine. HCCI engines take advantage of the high compression ratio and heat release rate and thus exhibit high efficiency found in compression ignition engines. In modern research, simulation has be come a powerful tool as it saves time and also economical when compared to experimental study. Engine simulation has been developed to predict the performance of a homogeneous charge compression ignition engine. The effects of compression ratio, cylinder pressure, rate of pressure rise, flame temperature, rate of heat release, and mass fraction burned were simulated. The simulation and analysis show several meaningful results. The objective of the present study is to develop a combustion characteristics model for a homogeneous charge compression ignition engine running with isooctane as a fuel and effect of compression ratio.

Homogeneous charge compression ignition (HCCI) engines are being considered as an alternative to diesel engines. The HCCI concept involves premixing fuel and air prior to induction into the cylinder (as is done in current spark-ignition engine) then igniting the fuel-air mixture through the compression process (as is done in current diesel engines). The combustion occurring in an HCCI engine is fundamentally different from a spark-ignition or Diesel engine in that the heat release occurs as a global autoignition process, as opposed to the turbulent flame propagation or mixing controlled combustion used in current engines. The advantage of this global autoignition is that the temperatures within the cylinder are uniformly low, yielding very low emissions of oxides of nitrogen (NOx, the chief precursors to photochemical smog). The inherent features of HCCI combustion allows for design of engines with efficiency comparable to, or potentially higher than, diesel engines. While HCCI engines have great potential, several technical barriers exist which currently prevent widespread commercialization of this technology. The most significant challenge is that the combustion timing cannot be controlled by typical in-cylinder means. Means of controlling combustion have been demonstrated, but a robust control methodology that is applicable to the entire range of operation has yet to be developed. This research focuses on understanding basic characteristics of controlling and operating HCCI engines. Experiments and detailed chemical kinetic simulations have been applied to the characterize some of the fundamental operational and design characteristics of HCCI engines. Experiments have been conducted on single and multi-cylinder engines to investigate general features of how combustion timing affects the performance and emissions of HCCI engines. Single-zone modeling has been used to characterize and compare the implementation of different control strategies. Multi-zone modeling has been applied to investigate combustion chamber design with respect to increasing efficiency and reducing emissions in HCCI engines.

This paper deals with experimental investigations of homogeneous Charge Compression Ignition (HCCI) engine using hydrous methanol as a primary fuel and Diethyl ether (DEE) as an ignition improver. In the present work a regular diesel engine has been modified to work as HCCI engine. The hydrous methanol is inducted and DEE is injected into a single cylinder engine.Hence,in the present investigation HydrousMethanol is used with 15% water content in HCCI engine and its performance and emission behavior is documented.Here, Diethyl ether (DEE) is used as an ignition improver and admitted along with Methanol fuel through separate fuel admission device. The auto-ignition of Methanol is enabled by DEE. The quantity of DEE varies with respect to the load. In this study, the experiments are conducted independently and the effect of the HydrousMethanol on the engine operating limit, heat release rate and exhaust emissions at different load conditions are investigated. The investigation also proves that the HydrousMethanol with DEE operation reduces the emission ofNOx and smoke to an extreme low level which is not possible by the direct injection CI engine. Thus the HydrousMethanol with 15% water content and DEE operate well in HCCI engine without any operational problem. Therefore, it is beneficial to use hydrous methanol-DEE HCCI mode while using hydrous methanol in internal Combustion Engines.

For many years, researchers have been trying to develop internal combustion engines with increased efficiency, while striving to satisfy stricter environmental regulations that limit the constituents of harmful emissions being produced. Homogenous charge compression ignition (HCCI) engines have provided a window of opportunity to make this happen since they incorporate the most ‘attractive’ features from both the standard spark-ignition engine and the compression-ignition engine, resulting in higher efficiencies and cleaner emissions. The main challenge of HCCI combustion is that it is triggered by the auto-ignition of the air-fuel mixture during compression, therefore, making it difficult to control while ensuring maximum efficiency. This research project aims to apply HCCI technology in an attempt to improve the performance of stationary power generation systems in Qatar by developing a low emission – high efficiency natural gas engine. In this poster, we will demonstrate the experimental setup that has been installed and the control strategy that will be used to control ignition timing. The test bench is made up of a single-cylinder engine with intake and exhaust piping system, as well as sensory equipment. The engine is controlled and monitored by a data acquisition (DAQ) computer system. We will show that initial performance data, obtained under full load and at different engine speeds, are in accordance with the performance data from the manufacturer. In addition, a mathematical pressure model has been developed and compared with experimental data, which will be used as the primary input for the feedback control mechanism. We will explain the process in which engine control algorithms use instantaneous cylinder pressure measurements and appropriate thermodynamic relationships to determine the rate of heat release (ROHR). Measured ROHR will then be compared with acceptable rates and controlled using exhaust gas recirculation (EGR) and intake and exhaust manifold pressures and temperatures. Finally, further work to implement HCCI natural gas fueled engine will be discussed.

Diethyl ether as an ignition improver for biogas homogeneous charge compression ignition (HCCI) operation - An experimental investigation