High Efficiency, Low Emissions Homogeneous Charge Compression Ignition (HCCI) Engines

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 (< 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.

<div class="section abstract"><div class="htmlview paragraph">The Homogeneous Charge Compression Ignition (HCCI) combustion eliminates the issues of higher particulate matter and nitrogen oxides emissions that prevail in the traditional compression ignition (CI) combustion mode. The complete replacement of traditional fuels with renewable fuels for internal combustion engines is challenging because significant infrastructure changes in the production and delivery systems are required to ensure renewable fuel availability and economic feasibility. Thus, the use of renewable acetone blended with traditional gasoline has been proposed in the present study to smoothen the transition from the traditional CI to the HCCI engines. HCCI experiments were performed in a light-duty diesel engine at 1500 rpm rated speed. By varying the volumetric proportion of the acetone in the gasoline from 20% to 40%, the HCCI engine load range from 20%-60% was achieved, significantly higher than the limited diesel HCCI load range of 20%-38%. An ignition-quality enhancer, 2-Ethylhexyl nitrate, at 6 vol.%, was blended in the acetone-gasoline to prevent the higher cyclic IMEP fluctuations at the lower engine loads. The empirical correlation of the start of combustion (CA10) established on a rapid compression machine facility was validated for the HCCI engine. The combustion phasing (CA50) was predicted using CA10 and fresh air equivalence ratio. A double-Weibe function was developed to characterize specifically the high-temperature heat release rate during the HCCI combustion and determine the extent of its fast-burning core region. An in-depth energy balance study was conducted to elucidate the reason for the indicated thermal efficiency trends. The acetone-gasoline-fuelled HCCI engine generated smoke and nitrogen oxides emissions that were less than 0.0007 g/kW-h and 2.5 g/kW-h, respectively, at all the engine loads. This study concluded that lower exhaust emissions could be obtained without compromising engine performance when the acetone-gasoline blends are used as fuels for operating the HCCI engine.</div></div>

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.

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.

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.

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) 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.

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.

&lt;div class="htmlview paragraph"&gt;Autoignition of a homogeneous mixture is very sensitive to operating conditions, therefore fast control is necessary for reliable operation. There exists several means to control the combustion phasing of an Homogeneous Charge Compression Ignition (HCCI) engine, but most of the presented controlled HCCI result has been performed with single-input single-output controllers. In order to fully operate an HCCI engine several output variables need to be controlled simultaneously, for example, load, combustion phasing, cylinder pressure and emissions. As these output variables have an effect on each other, the controller should be of a structure which includes the cross-couplings between the output variables. A Model Predictive Control (MPC) controller is proposed as a solution to the problem of load-torque control with simultaneous minimization of the fuel consumption and emissions, while satisfying the constraints on cylinder pressure. One of the major motivations for using MPC is that it explicitly takes the constraints into account. When operating an HCCI engine there are several contraints present, for example on the cylinder pressure and on the emissions. A drawback of MPC is the potentially large on-line computational effort, which has historically limited its application to relative slow and/or small applications. Today, MPC can be applied in relative fast systems, and we will demonstrate that it can be used for control of HCCI engine dynamics on a cycle-to-cycle basis.&lt;/div&gt; &lt;div class="htmlview paragraph"&gt;As feedback signal of the combustion phasing, the crank angle for 50% burned, based on cylinder pressure, is used. In the control design of the MPC controllers (one for each cylinder), dynamic models obtained by system identification were used. This paper presents cycle-to-cycle cylinder individual control results from a six-cylinder HCCI engine using a Variable Valve Actuation (VVA) system and MPC controllers.&lt;/div&gt;

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.

Effect of hydrogen sulfide content on the combustion characteristics of biogas fuel in homogenous charge compression ignition engines

Homogeneous Charge Compression Ignition (HCCI) engines are considered an emerging internal combustion technology with significant potential for enhancing fuel efficiency and lowering emissions compared to traditional Spark Ignition (SI) and Compression Ignition (CI) engines. By igniting a homogeneous air-fuel mixture through compression without the need for a spark plug, HCCI engines achieve a more uniform and complete combustion process, resulting in lower NOx and particulate matter (PM) emissions. Despite these advantages, challenges such as limited control over combustion timing, susceptibility to knocking, and the generation of unburned hydrocarbons have hindered widespread adoption. Recent advancements in engine control strategies and hybrid technologies offer promising solutions to these critical issues, potentially enabling broader application of HCCI engines in both the automotive industry and power generation sectors. As research continues to address these challenges, HCCI engines may play a pivotal role in the future of more ‘green’ internal combustion systems with higher efficiency.

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.

Concerns from both society and the government about the pollutants from automobile exhaust is becoming more and more noticeable in recent years. Compared with the engines mostly used currently, which are gasoline engines and diesel engines, the HCCI engine has ameliorated not only the problem of pollutant emissions but also efficiency to a large extent. This paper provides an in-depth analysis of Homogeneous Charge Compression Ignition (HCCI) engines. It first introduces the fundamental processes governing HCCI combustion and illustrates its working mechanism. While HCCI engines promise heightened efficiency, reduced emissions, and fuel versatility, they also present challenges such as combustion timing and related emissions. Commercial implementations by Nissan and Honda are discussed, shedding light on real-world applicability. Furthermore, the potential amalgamation of biodiesel with HCCI is explored, signaling a promising future for renewable fuels in advanced combustion engines. Despite the rise of hybrid vehicles, the unique benefits of HCCI position it as a significant player in future transportation. This paper emphasizes the necessity of ongoing research to overcome HCCIs challenges, ensuring it remains at the forefront of green automotive solutions.

Homogeneous charge compression ignition (HCCI) engines have low nitrogen oxide and particulate matter engine-out emissions but have higher unburned hydrocarbon and carbon monoxide emissions than the conventional spark ignition (SI) and diesel engines do. Only for sufficiently high exhaust gas temperatures can an exhaust after-treatment be used; thus a low exhaust gas temperature in certain operating conditions can limit the operating range in HCCI engines. The influences of the engine conditions on the exhaust gas temperature in a single-cylinder experimental engine are investigated at 340 steady state operating points. The variation in the exhaust gas temperature is also studied under transient conditions and during mode switching between SI and HCCI combustion. For the conditions tested, a significant number of data have an exhaust gas temperature below 300°C which is below the light-off temperature of typical catalytic converters on the market. Three different categories of engine variables are recognized and classified by how the exhaust temperature is affected by changing that variable. The first category is defined as the primary variables (e.g. the intake pressure and the fuel octane number) for which the location of ignition timing is the dominant factor in influencing the exhaust temperature. The other groups include compounding variables such as the engine speed and opposing variables such as the intake temperature, the coolant temperature, and the equivalence ratio. In addition, experimental results show that the exhaust temperature for HCCI engines is not strongly dependent on the engine load, unlike that for SI engines where the engine load is a main factor in determining the exhaust temperature.