Homogeneous Charge Compression Ignition Engine Research Articles

Construction of reduced oxidation mechanisms of polyoxymethylene dimethyl ethers (PODE1–6) with consistent structure using decoupling methodology and reaction rate rule

Due to high oxygen content and lack of CC bond, polyoxymethylene dimethyl ethers (PODEn) have become desired fuel additives to simultaneously reduce nitrogen oxides (NOx) and soot emissions. However, there is a vacancy of reduced reaction mechanisms to describe the long-chain PODEn (n>3) combustion for engine simulations. This study aims at the construction of reduced mechanisms for the series of PODE1–6 with a consistent structure based on the decoupling methodology and reaction rate rule. First, the reduced mechanisms of PODE1–2 are constructed using the reaction class-based global sensitivity analysis and the decoupling methodology. In the reduced mechanisms of PODE1–2, the skeletal fuel-related sub-mechanism is integrated with a detailed H2/CO/C1 sub-mechanism and a reliable reduced C2–C3 sub-mechanism. Then, due to the similar molecular structure, the skeletal fuel-specific sub-mechanisms of the long-chain PODE3–6 are constructed based on the benchmark fuel of PODE2. The kinetic parameters of the reactions in the skeletal fuel-specific sub-mechanism of PODE3–6 are obtained using the modified linear lumping method and the reaction rate rule assumption. Through the approach proposed in this study, the reduced mechanisms of long-chain PODEn can be effectively constructed based on the chemistry of short-chain PODEn, especially for PODE5–6 with no available detailed mechanisms so far. The final reduced mechanism for the complete series of PODE1–6 only consists of 92 species and 389 reactions. To validate the predictions of the reduced mechanism, extensive comparisons are carried out including ignition delay times in shock tubes, major species concentrations in jet-stirred reactors, and laminar flame speeds and flame species concentrations in premixed laminar flames. Moreover, the measurements of homogeneous charge compression ignition (HCCI) engines fueled with PODE2–4 and PODE3–6 are used for the validations of in-cylinder pressure, heat release rate, and emissions. The overall performance of the reduced mechanism of PODE1–6 is satisfactory under wide operating conditions. This present approach can also be extended to build compact-size reduced mechanisms for the fuels with similar molecular structures, even though no detailed mechanism is available.

Application of machine learning tools for constrained multi-objective optimization of an HCCI engine

Because of strict emission regulations, significant efforts are made by researchers to reduce the pollutants from internal combustion engines. Homogeneous mixture of fuel and air in Homogeneous Charge Compression Ignition (HCCI) engine results in lower amounts of thermal NOx while CO and HC emissions would be higher in this process. Besides, performance instability due to knock and misfire is another problem that HCCI engines are facing. In this paper, machine learning tools have been implemented to learn the behavior of a single-cylinder engine using three different fuels with the HCCI strategy. Changes in six objective functions with engine Inlet Valve Closing (IVC) temperature and air-fuel equivalence ratio are studied with the help of an Artificial Neural Network (ANN). Those objective functions are thermal efficiency, combustion efficiency, IMEP, together with NOx, CO, and HC emissions. A multi-objective optimization algorithm based on a decomposition method and genetic algorithm is used to identify the best operating condition of studied fuels. Results show that HCCI engine fueled with Ethanol and Methanol could produce significantly lower HC and CO emissions at their optimum point. However, the produced NOx would be higher in these cases comparing to the engine fueled with CNG. The genetic algorithm indicates that the optimum point of operation for CNG-fueled engine is TIVC ≈ 445 K while λ ≈ 2.25. In contrast, for the Ethanol-fueled case, this optimum point is located in the IVC temperature of ≈450 K and λ ≈ 2.75. The TOPSIS point is located in minimum air-fuel equivalence ratio and lower IVC temperatures (TIVC ≈ 420 K) when the engine is being operated with Methanol as fuel.

Combustion Characteristics of Biogas Fuel Using Particularly Simplified Reaction Mechanism for HCCI Engines

Renewable energy resources like biogas fuel are highly needed to overcome the increasing demands on energy and to allow more efficient power transformation. Biogas is not investigated adequately in homogenous charge compression ignition (HCCI) engines and no specific chemical kinetics were proposed for its combustion in HCCI engines. In this study, a reaction mechanism had been proposed to simulate biogas combustion in HCCI engines. A combined mechanism reduction algorithm, using a graph-based approach and sensitivity analysis, was used to reduce a full detailed mechanism for C1-C4 hydrocarbon fuels. The resulted mechanism consists of 42 species and 328 reactions that were selected to predict the ignition delay time of the HCCI ignition process. The new mechanism was implemented in a modified multizone combustion model using CANTERA flow reactions and MATLAB software. Many combustion parameters, including pressure and temperature profiles, ignition time, produced work, and heat release rate, were estimated. It was found that HCCI engines fueled with biogas can be an effective option for power generation applications at wide range of CH4-CO2 ratios. Furthermore, the reaction mechanism showed high ability in predicting the experimental data at HCCI operation conditions over a wide range of temperature (500–2,000 K) and equivalence ratios (0.4–1.8). This allows further investigations of the mechanism for combustion and emissions prediction at many different operation conditions.

The examination of injection strategies of jet propellant-8 for compression ignition engine with a low compression ratio

Jet Propellant-8 (JP-8) is used as a fuel for standard CI engine instead of diesel oil, especially in military applications on a large scale. For all such applications, the engine regulation parameters are optimal for diesel oil. The properties of kerosene-type fuel, encourage to test different strategies of mixture creation and combustion modes which could be more effective for JP-8 than these elaborated for diesel oil. The paper describes an experiment focused on finding an injection strategy for effective application of JP-8 to a CI engine with low compression ratio. To find an effective way of JP-8 application, the search described in the paper started from the investigation of Low Temperature Combustion (LTC) possibilities, including Homogeneous Charge Compression Ignition (HCCI) engine operation. It led to Partially Premixed Combustion (PPC) with the injection synchronised with the start of mixing controlled phase of combustion. It is also presented how small changes in the injection sequence could heavily influence the combustion phases and very significantly modify the combustion process. For the tests, a naturally aspirated AVL research engine equipped with a common rail system was adapted. The low compression ratio (CR=12:1) was applied. The experiment excluded Exhaust Gas Recirculation (EGR) and mixture dilution with the air. The paper contains the comparison of JP-8 combustion parameters, engine performance and emissions parameters obtained for different injection strategies.

Proposal and analysis of a novel cooling-power cogeneration system driven by the exhaust gas heat of HCCI engine fuelled by wet-ethanol

A novel combined power and cooling cycle consisting of the ejector refrigeration cycle (ERC) and organic Rankine cycle (ORC) is proposed to enhance the overall efficiency of wet-ethanol fuelled homogeneous charge compression ignition (HCCI) engine. The proposed combined system of cooling-power cogeneration was simulated by Engineering Equation Solver (EES) software. Combined system responses to altering the operative conditions on the energy and exergy performances are ascertained to obtain guidance for system design. The results are computed for R134a, R290, and R600a working fluids. Increase in turbocharger pressure ratio from 2.5 to 3.5 raises the thermal efficiency of cooling-power cogeneration from 47.87% to 50.09% when R134a is used as working fluid. Cooling capacity and exergy of refrigeration are decreased by greater than 2.0% in case of R134a operated system when the vapor generator pressure is elevated from 1800 kPa to 2200 kPa. Increase in evaporator pressure of ERC from 327.4 kPa to 348.7 kPa is greatly beneficial to thermodynamic performance of cogeneration and its cooling capacity is improved by 11.34% when R134a is utilized as the working. When PEvap rises from 175.7 kPa to 186.9 kPa and R600a is employed as the working fluid, the cooling capacity is increased by 12.58%.

Research on knock recognition of coal-based naphtha homogeneous charge compression ignition engine based on combined feature extraction and classification

The purpose of this study is to investigate combustion characteristics and knock recognition of HCCI engines fueled with coal-based naphtha by analyzing in-cylinder pressure. The in-cylinder pressures of knock and normal combustion at two different intake temperatures (Tin) of 60 °C and 90 °C were collected on a modified diesel engine, characteristic vector was constructed from the in-cylinder pressure signal based on empirical mode decomposition (EMD) and sample entropy (SampEn), and a support vector machine (SVM) classifier was used to recognize knock. The results show that in-cylinder pressure, heat release rate (HRR), in-cylinder temperature, pressure rise rate (PRR) and pressure rise acceleration (PRA) change steadily in normal combustion. With occurrence of knock, they have a sharp rise and huge fluctuations. HRRmax, PRRmax, and PRAmax are greatly increased, and the corresponding phase is significantly advanced, especially in high-temperature stage. When Tin is 90 °C, PRAmax reaches 1.174 MPa/°CA2, which is an increase of 854.47% compared to normal combustion. However, the coefficient of variation for peak pressure (COVPmax) of two Tins show completely opposite results. At Tin of 60 °C, COVPmax increases from 3.95% to 4.71%, while at Tin of 90 °C, COVPmax reduces from 3.08% to 1.52%. Moreover, knock recognition achieves the best classification result at Tin of 60 °C. The average classification accuracy reaches 91.35%, and the best classification accuracy reaches 99.67%. This shows that feature extraction method based on EMD and SampEn has excellent classification performance for knock recognition of coal-based naphtha HCCI engines.

Enabling robust simulation of polyoxymethylene dimethyl ether 3 (PODE3) combustion in engines

PODE3 reaction mechanism developments are still in the early stages with very limited research. In particular, reaction mechanisms to characterize PODE3 combustion are neither sufficiently compact nor robust for 3D numerical simulations. Hence, the current work seeks to develop a compact yet reliable PODE3 reaction mechanism, embedded with appropriate chemistry to describe polycyclic aromatic hydrocarbon reactions. A decoupling methodology has been employed to achieve the desired outcome. The final mechanism comprises only 120 species and 560 reactions even after including components of diesel and gasoline surrogates. It has been validated with ignition delay times, laminar flame speeds, jet-stirred reactor species concentration profiles, flame species concentration profiles, extinction strain rates, heat release rates in constant volume combustion chamber, homogeneous charge compression ignition engine combustion, and direct injection compression ignition engine combustion. In a numerical investigation conducted using gasoline/diesel/PODE3 blends, soot emissions are observed to decrease with PODE3 increment, which establishes PODE3 as a promising additive. Intriguingly, the current study has also discovered that with 15% PODE3 addition, soot and its precursors will increase in concentration during combustion, though this effect will be outweighed by oxidative effects towards the end. Overall, the new mechanism has been proven suitable and feasible for engine simulations.

Exergetic evaluation of operation results of 5-kW-class SOFC-HCCI engine hybrid power generation system

A solid oxide fuel cell (SOFC)-based hybrid power generation system using homogeneous charge compression ignition (HCCI) was previously proposed, based on which a proof-of-concept test has already been conducted by the Korea Institute of Machinery and Materials. In this study, energy and exergy analyses were performed to evaluate the experimental data obtained from the proof-of-concept test of the SOFC-HCCI engine hybrid system. In the analyses, particular attention is paid to the SOFC stack, HCCI engine, balance of plant (BOP) hot-box subsections and, accordingly, the energy and exergy flows within and between the above subsections. For the BOP hot-box, the energy and exergy analyses reveal different results. The energy analysis demonstrated that 75.1% of the transferred heat was recovered by the BOP components and pipes; only 25% of the heat, i.e., 638 W, was lost. However, the exergy analysis identified that only 35.1% of the transferred exergy was recovered; thus, 64.9% of the exergy was destroyed. Based on the energy and exergy analysis results, it is observed that the amount of exergy destruction exceeds the heat loss as the latter contributes to the former; this is in addition to the exergy destruction due to the irreversibility of the heat transfer between the components located in the BOP hot box. Based on the analyses of the entire system, the various heat losses and exergy destruction are quantitatively identified. In particular, significant heat loss and exergy destruction occur in the engine, additional burner, and BOP components. To improve the efficiency of the system, the insulation of the system can be reinforced, thereby reducing heat loss and exergy destruction and burner usage can be minimized. This suggests that the heat losses from the system components, mostly in the HCCI engine, should be reduced or reused to improve the overall efficiency of the system.

Effect of Preheating Temperature and Fuel Properties on Combustion and Emission Characteristics of Homogeneous Charge Compression Ignition (HCCI) Engine

The homogeneous charge compression ignition (HCCI) engine is the promising technology to reduce the pollutants without affecting its performance and it is also proved by the many studies. This study investigates the performance and emission characteristics of HCCI engine fuelled with diesel –waste cooking oil (WCO) blends and also analysed the effect of air temperature and fuel properties on HCCI engine combustion. The experimental investigation was conducted with single cylinder DI diesel engine and it was slightly modified to port injection system for premixing the charge. The electric air heater was adopted in suction pipe to preheat the inlet air. The experimental investigation conducted in two phases, in the first phase the conventional DI diesel engine was tested with different fuel blends such as B25, B50, B75 and B100 and notes the readings. In the next phase, HCCI engine was operated with same blend ratios. During the experimentation on HCCI engine, the suction air temperature was varied between 40⁰C to 90⁰C. From the experimental results, it was found that the HCCI engine has emitted low NOx and smoke emissions at 80⁰C of air temperature for all the blends. Whereas the HCCI engine emitted more carbon monoxide (CO) and hydrocarbon (HC) emissions due to lean mixture causes misfiring in the chamber. In addition, it is also noted that the value of CO and HC has been varied with diesel –WCO blends. The specific fuel consumption (SFC) is increased for diesel and biodiesel fuel in HCCI engine compared to compression ignition (CI) engine

A high-efficiency scheme for waste heat harvesting of solid oxide fuel cell integrated homogeneous charge compression ignition engine

Facing the energy shortage and environmental pollution problems in the world, a high-efficiency fuel cell scheme combined with waste heat recovery is regarded as an optimal selection of auxiliary power generation equipment for ships. In this study, a novel system, comprising solid-oxide-fuel-cell-preheating subsystem, homogeneous charge compression ignition engine and organic Rankine cycle, is designed and analysed. First, the mathematical model is established and verified to ensure the reliability of simulation results. Then, the effect of relevant parameters on homogeneous charge compression ignition engine performance is observed, and the optimal zeotropic working fluid of organic Rankine cycle is determined according to the exhaust temperature. Finally, the thermodynamic and economic analysis are carried out. The results indicate that the performance of the new system is better than that of the traditional combined system using gas turbine. Thermal efficiency and exergy efficiency of the system are more than 63.6% and 61.3%, which is about 18.76% and 17.95% higher than that of simple cell. In addition, the payback time is about 2.98 years, which is about half of the traditional combined system and can fully meet the economic requirements. This novel system can be a new selection of marine auxiliary power generation equipment.

Effects of EGR and Alternative Fuels on Homogeneous Charge Compression Ignition (HCCI) Combustion Mode

We present in this article an analysis of the impacts of the exhaust gas recirculation (EGR) and alternative fuels on HCCI combustion mode. The objective is to reduce the pollutant emissions below the levels of established pollution standards. The ANSYS CHEMKIN-Pro software and the combined chemical kinetics mechanism were used to perform simulations for a closed homogeneous reactor under conditions relevant to HCCI engines. The calculation process is based on one single-zone in the combustion chamber. Numerical simulation has proven the ability of the models adopted, which use the essential mechanisms of the fuel combustion process, to reproduce, among other things, the evolution of the formation of chemical species. This study showed that adding hydrogen (H2) to methane (CH4) is an interesting alternative fuel because it reduces ignition time. It was concluded that an increase of EGR rate conducts to a slower combustion process, lower temperatures, and the reduction of nitrogen oxide (NOX) emissions.

A Comparative Numerical Study of the Combustion Performance of the Syngas-Fueled HCCI Engine Using a Toroidal Piston, Square Bowl Piston, and Flat Piston Shape at Different Loads

Abstract This study analyzes the combustion performance of a syngas-fueled homogenous charge compression ignition (HCCI) engine using a toroidal piston (baseline piston), square bowl, and flat piston shape, at low, medium, and high loads, with a constant compression ratio of 17.1. In this study, the square bowl shape is optimized by reducing the piston bowl depth and squish area ratio (squish area/cylinder cross-sectional area) from 34 to 20, 10, and 2.5% and compared with the flat piston shape and toroidal piston shape. This HCCI engine operates under an overly lean air–fuel mixture condition for power plant usage. ansys forte cfd package with GRI Mech3.0 chemical kinetics is used for combustion analysis, and the calculated results are validated by the experimental results. All simulations are accomplished at maximum brake torque (MBT) by altering the air–fuel mixture temperature at intake valve closing (IVC) (TIVC) with a constant equivalence ratio of 0.27. This study reveals that the main factors that affect the start of combustion (SOC), maximum pressure rise rate (MPRR), combustion efficiency, and thermal efficiency by changing the piston shape are the squish flow and reverse squish flow effects. Therefore, the square bowl piston D is the optimized piston shape that offers low MPRR and high combustion performance for the syngas-fueled HCCI engine, due to the weak squish flow and low heat loss rate through the combustion chamber wall, respectively, when compared with the other piston shapes of square bowl piston A, B, and C, flat piston, and toroidal (baseline) piston shape.

Investigation of the main exhaust emissions of HCCI engine using a newly proposed chemical reaction mechanism for biogas fuel

In this study, the main exhaust emissions from biogas fueled homogenous charge compression ignition (HCCI) engine model were investigated using a newly proposed reaction mechanism. The study was conducted by reducing a full detailed reaction mechanism using a combined algorithm built based on the graph-based approach. The exhaust emissions were estimated using a modified multi-zone combustion model. The chemical kinetics model was built using CANTERA reaction flow package and MATLAB® software. The new reduced mechanism (42 species and 228 reactions) showed higher agreement with the experimental data than the GRI-Mech 3.0 mechanism (53 species and 325 reactions). The effects of many parameters on emissions, including the equivalence ratio (0.25–0.4), CH4% (30%–80%), and the inlet intake temperature (420 K–500 K), were investigated. The results indicated that increasing the equivalence ratio above 0.25 increases the NOx emissions significantly as it increases the combustion peak bulk temperature. The same observation was obtained as the intake temperature and the CH4 content were increased above 420 K and 30% respectively and for the same reason. However, CO and unburned hydrocarbons (HC) emissions were decreased significantly as the equivalence ratio increased above 0.25, while they slightly changed with increasing the CH4% and the inlet intake temperature.

Effects of operating parameters on the performance, emission and combustion indices of a biogas fuelled HCCI engine

This study discusses the operation of a Homogeneous Charge Compression Ignition (HCCI) engine using simulated biogas and diethyl ether (DEE) as the primary and secondary fuels respectively. Performance, emission and combustion parameters are measured for various biogas flow rates (8–16 litre/min), composition (50 to 100% methane), intake temperatures (35–80 °C) and loads (20 to 90% of full load). A comparison of injecting DEE at the intake port (port injection) and 7 cm upstream (manifold injection) is also presented. It was demonstrated that at high flow rates and/or with high methane content, biogas can effectively substitute DEE and provide up to 60% of the total energy input. However, the use of lower biogas flow rates and methane fraction resulted in better thermal efficiency (as high as 26%) as well as lower HC emissions. HCCI operation offered simultaneously low NOx (< 0.2 g/kWh) and smoke (~1%). Intake heating ensured better performance and emissions, although it increased the tendency to knock. In general, manifold injection provided superior engine output compared to port injection. The knock limit of HCCI operation could be effectively extended by employing high biogas flow rates and/or methane enrichment. ANOVA study showed that biogas flow rate had a strong influence on most engine output parameters. While methane fraction correlated well with combustion indices, engine torque had a significant effect on thermal efficiency and emissions.

Potential of Semi-Empirical Heat Transfer Models in Predicting the Effects of Equivalence Ratio on Low Temperature Reaction and High Temperature Reaction Heat Release of an HCCI Engine

In this paper, the influence of equivalence ratio on the low-temperature reaction heat release (LTR-HR) and high-temperature reaction heat release (HTR-HR) of homogeneous charge compression ignition engine has been experimentally and numerically examined. The numerical study was performed using zero-dimensional (0D) single-zone model by considering the chemical kinetic of fuel combustion. Annand, Woschni, Hohenberg, Chang (Assanis), and Hensel semi-empirical heat transfer models were employed in the 0D single-zone simulations. In this study, the in-cylinder pressure, rate of heat release, LTR-HR and HTR-HR were investigated. The Hensel heat transfer model was the only model that predicted the combustion in all of the operating conditions. The Hohenberg model properly recognized the effects of equivalence ratio changes on the HTR-HR.

Experimental investigation of strategies to enhance the homogeneous charge compression ignition engine characteristics powered by waste plastic oil

In the present-day scenario, the regulations over vehicle emissions are highly stringent, and the manufacturers are struggling to satisfy the emission norms. Waste plastic oil (WPO) powered conventional compression ignition (CI) engine discharge higher oxides of nitrogen emission. The utilization of WPO as a sole fuel in homogeneous charge compression ignition (HCCI) engine would satisfy both energy demand and emission norms. The present study demonstrates the effects of different intake air temperatures (IAT) and injection pressures (IP) of WPO on the HCCI engine’s performance and combustion characteristics. The results revealed that the WPO fueled CI engine showed greater BTE when correlated to WPO powered HCCI engine. In the HCCI mode of operation, the elevated IAT led to the advanced start of combustion (SOC). It shortened the combustion due to an increase in post-combustion temperature and cylinder pressure. WPO operated homogeneous charge mode with IAT of 90 °C resulted in better BTE and lesser unburnt hydrocarbon (UBHC), smoke, and carbon monoxide (CO) emission than IAT atmospheric conditions. The HCCI engine with elevated IAT of 80 °C, 90 °C, and 100 °C drastically reduced the NOx emission by 45.5%, 41.9%, and 40.04% than standard CI engine fueled with WPO+- respectively. Among various IPs of WPO, IP of 8 bar revealed 3.08% higher BTE with 11.2%, 16.6%, 14.7% decrease in CO, UBHC, and smoke emission, respectively. At the optimum condition of IP and IAT in the HCCI engine, the BTE was closer to that of the WPO powered CI engine, and also ultra-lean NOx and smoke emissions were noticed.

Study of methane enrichment in a biogas fuelled HCCI engine

Biogas has been a promising alternative fuel for IC engines. However, its CO2 content reduces calorific value and ignitability. The CO2 fraction of raw biogas can be separated out by various techniques, which are collectively called methane enrichment. The present study explores the effect of methane enrichment on the output parameters of a Homogeneous Charge Compression Ignition (HCCI) engine. A single cylinder CI engine is altered for this purpose. Biogas (CH4 + CO2) is supplied along with air. Diethyl Ether (DEE) is used as the secondary fuel to initiate auto-ignition. The effects of injecting DEE at the inlet port and upstream in the intake manifold are also compared. Performance, emission and combustion characteristics such as brake thermal efficiency, equivalence ratio, HC, CO, CO2, NOx and smoke emissions, start and duration of combustion, in-cylinder pressure and maximum heat release rate are compared for operation with raw biogas (50% methane) and methane enriched biogas (100% methane) for various biogas flow rates and engine torques. Results show that methane enrichment enhances brake thermal efficiency by up to 2% compared to raw biogas. Methane enrichment advances and speeds up combustion. HC, CO and CO2 emissions, maximum cylinder pressure and maximum heat release rate are also improved with methane enrichment. Ultra-low NOx and smoke emissions can be obtained using raw biogas as well as methane enriched biogas. Low biogas flow rates provide better brake thermal efficiency and HC emissions. Manifold injection of DEE enhances brake thermal efficiency by up to 2% compared to port injection by virtue of greater mixture homogeneity.

The thermal and auto-ignition performance of a homogeneous charge compression ignition engine fuelled with diethyl ether and ethanol blends

Abstract This study aims to numerically investigate the thermal and auto-ignition performance of a Homogeneous Charge Compression Ignition (HCCI) engine fuelled with diethyl ether and ethanol blends at different inlet air temperatures and lambda values. In this study, DEE and DEE/ethanol blends with different volume percentages, such as 85% DEE/15% ethanol (D85E15) and 70% DEE/30% ethanol (D70E30) was used as test fuels. A four-stroke single-cylinder HCCI engine was designed to use reduced fuel chemistry to create a zero-dimensional single-zone model. The single-zone combustion model was developed with the first law of thermodynamics as a differential form. The inlet air temperature ranged from 360 K to 420 K at 15 K intervals, and the lambda ranged from 1.5 to 2.5 at 0.25 intervals to evaluate the combustion control in the HCCI engine. A numerical study was carried out at an engine speed of 1200 rpm. The numerical validation model results were well agreed with reported experimental results, and the significant trends of the combustion phases were varied with a minimum error of 5%. The numerical results show that the in-cylinder pressure and heat release rate are decreased for all test fuels with the increasing lambda. The combustion phase was found to be advanced, and the combustion duration was expanded with increasing inlet air temperature. Increasing the ethanol proportion in the test fuel delayed the start of combustion. For D85E15 and D70E30 at lambda of 2 and inlet air temperature of 420 K, the indicated mean effective pressure was increased by about 12.6% and 6.10 bar. Furthermore, with DEE and D85E15 at a lambda of 2, the indicated thermal efficiency was increased by approximately 11.4% and 49.17%. It is concluded that the combustion and performances characteristics for the HCCI engine are significantly affected by DEE and ethanol fuel blends.

Varying Ignition Quality of a Fuel for a HCCI Engine Using a Photochemically-Controlled Additive: The Development of a ‘Smart’ Fuel

This study examines the possibility to provide control over ignition timing in a homogeneous charge compression ignition engine (HCCI) using a fuel additive whose molecular structure can be adapted upon exposure to UV light. The UV adapted molecule has a greater influence on retarding ignition than the original molecule, hence the ignition time can be modulated upon expose to UV light. The new fuel is referred to as a ‘smart fuel’. The fuel additive is in the form of 1,3-cyclohexadiene (CHD), upon UV exposure it undergoes electro-cyclic ring opening to form 1,3,5-hexatriene (HT). Various solutions of iso-octane, n-heptane and CHD have been irradiated by UV light for different amounts of time. CHD to HT conversion was examined using gas chromatography coupled with mass spectrometry. A primary reference fuel (PRF) mixture of 90% iso-octane and 10% n-heptane was used as a baseline in an optically accessible combustion chamber in a large bore, single cylinder compression ignition engine. The engine was operated in HCCI mode, using early injection to provide homogeneous mixture and utilized heated and compressed air intake. Following this a PRF with 5% CHD was used in the engine. A PRF with 5% CHD was then irradiated with UV light for 240 min, resulting in a PRF mixture containing 1.72% HT, this was then used in the engine. The HT containing PRF had a much later start of combustion compared with the CHD containing PRF, which in turn had a later start of combustion compared with the PRF baseline. This study has successfully validated the concept of using a photo-chemical ‘smart’ fuel to significantly change the ignition quality of a fuel in HCCI mode combustion and demonstrated the concept of on-board ‘smart fuel’ applications for ICE.

Experimental and Numerical Analysis on the Influences of Direct Fuel Injection Into Oxygen-Depleted Environment of a Homogeneous Charge Compression Ignition Engine

Abstract The oxygen-depleted environment in the recompression stroke can convert gasoline fuel into light hydrocarbons due to thermal cracking, partial oxidation, and water-gas shift reactions. These reformate species can influence the combustion characteristics of gasoline direct injection homogeneous charge compression ignition (GDI-HCCI) engines. In this work, the combustion phenomena are investigated using a single-cylinder research engine under a medium load. The main combustion phases are experimentally advanced by direct fuel injection into the negative valve overlap (NVO) compared with that of intake stroke under single/double-pulse injections. NVO peak in-cylinder pressures are lower than that of motoring due to the limited O2 concentration, emphasizing that endothermic reactions occur during the overlap. This phenomenon limits the oxidation reactions, and the thermal effect is not pronounced. The zero-dimensional chemical kinetics results present the same increasing tendencies of classical reformed species of rich mixture such as C3H6, C2H4, CH4, CO, and H2 as functions of injection timings. Predicted ignition delays are shortened due to the additions of these reformed species. The influences of the reformates on the main combustion are confirmed by three-dimensional computational fluid dynamics (CFD) calculations, and the results show that OH radicals are advanced under NVO injections relative to intake stroke injections. Consequently, earlier heat release and cylinder pressure are noticeable. Parametric studies on the effects of injection pressure, double-pulse injection, and equivalence ratio on the combustion and emissions are also discussed experimentally.