Homogeneous Charge Research Articles

Effect of Intake Air Temperature and Premixed Ratio on Combustion and Exhaust Emissions in a Partial HCCI-DI Diesel Engine

Homogeneous charge compression ignition (HCCI) is considered an advanced combustion method for internal combustion engines that offers simultaneous reductions in oxides of nitrogen (NOx) emissions and increased fuel efficiency. The present study examines the influence of intake air temperature (IAT) and premixed diesel fuel on fuel self-ignition characteristics in a light-duty compression ignition engine. Partial HCCI was achieved by port injection of the diesel fuel through air-assisted injection while sustaining direct diesel fuel injection into the cylinder for initiating combustion. The self-ignition of diesel fuel under such a set-up was studied with variations in premixed ratios (0–0.60) and inlet temperatures (40–100 °C) under a constant 1600 rpm engine speed with 20 Nm load. Variations in performance, emissions and combustion characteristics with premixed fuel and inlet air heating were analysed in comparison with those recorded without. Heat release rate profiles determined from recorded in-cylinder pressure depicted evident multiple-stage ignitions (up to three-stage ignition in several cases) in this study. Compared with the premixed ratio, the inlet air temperature had a greater effect on low-temperature reaction and HCCI combustion timing. Nonetheless, an increase in the premixed ratio was found to be influential in reducing nitric oxides emissions.

Effect of swirl ratio on charge convection, temperature stratification, and combustion in gasoline compression ignition engine

Various low-temperature combustion strategies (namely, homogeneous charge compression ignition, reactivity controlled compression ignition, and partially premixed charge compression ignition) have shown the potential to comply with upcoming and prevailing stringent emissions legislations. Low octane gasoline has emerged as an ideal fuel candidate for premixed charge combustion under diesel-like conditions in gasoline compression ignition (GCI) engines. GCI is an excellent technology to rectify future global energy demand imbalance, because it aims to replace diesel (which is in short supply) with low octane fractions/naphtha (which is in surplus supply) in compression ignition engines. However, this novel combustion concept requires modifications in the conventional design of diesel engines. The combustion chamber shape and in-cylinder flows play a crucial role in charge distribution and temperature stratification. Therefore, understanding the combined effect of combustion chamber geometry and in-cylinder flows is essential for future engine designs. GCI combustion engine simulations for varying swirl ratios (SRs) were performed in CONVERGE CFD software to understand the effect of in-cylinder air motion on the mixture stratification and combustion. A 1/7th sector geometry for a conventional re-entry piston bowl was modeled and then simulated. Two different mechanisms were used for model validation. The results indicated that the large-scale flow structures govern the fuel distribution in the combustion chamber. The charge convection because of increased swirl has a substantial effect on the combustion characteristics of the engine. A distinguished ignition kernel was observed for all test cases. An interfacial region with counter-rotating vortices formed a lean mixture zone, hindering flame propagation and combustion. A lower SR, shallow depth piston, and modifications to avoid flame quenching in the squish zone need to be further investigated to optimize the engine performance.

Machine Learning-Based Identification Strategy of Fuel Surrogates for the CFD Simulation of Stratified Operations in Low Temperature Combustion Modes

Many researchers in industry and academia are showing an increasing interest in the definition of fuel surrogates for Computational Fluid Dynamics simulation applications. This need is mainly driven by the necessity of the engine research community to anticipate the effects of new gasoline formulations and combustion modes (e.g., Homogeneous Charge Compression Ignition, Spark Assisted Compression Ignition) to meet future emission regulations. Since those solutions strongly rely on the tailored mixture distribution, the simulation and accurate prediction of the mixture formation will be mandatory. Focusing purely on the definition of surrogates to emulate liquid phase and liquid-vapor equilibrium of gasolines, the following target properties are considered in this work: density, Reid vapor pressure, chemical macro-composition and volatility. A set of robust algorithms has been developed for the prediction of volatility and Reid vapor pressure. A Bayesian optimization algorithm based on a customized merit function has been developed to allow for the efficient definition of surrogate formulations from a palette of 15 pure compounds. The developed methodology has been applied on different real gasolines from literature in order to identify their optima surrogates. Furthermore, the ‘unicity’ of the surrogate composition is discussed by comparing the optimum solution with the most different one available in the pool of equivalent-valuable solutions. The proposed methodology has proven the potential to formulate surrogates characterized by an overall good agreement with the target properties of the experimental gasolines (max relative error below 10%, average relative error around 3%). In particular, the shape and the end-tails of the distillation curve are well captured. Furthermore, an accurate prediction of key chemical macro-components such as ethanol and aromatics and their influence on evaporative behavior is achieved. The study of the ‘unicity’ of the surrogate composition has revealed that (i) the unicity is strongly correlated with the accuracy and that (ii) both ‘unicity’ and accuracy of the prediction are very sensitive to the high presence of aromatics.

Thermodynamic and Comparative Analysis of Ejector Refrigeration Cycle and Absorption Refrigeration Cycle Integrated Wet Ethanol-Fueled HCCI Engine for Cogeneration of Power and Cooling

Abstract This study attempted for the proposal and analysis of a combined cycle that consists of a wet ethanol-fueled and turbocharged homogeneous charge compression ignition (HCCI) engine coupled to ejector refrigeration cycle (ERC) and absorption refrigeration cycle (ARC) for the simultaneous generation of two distinct outputs, namely, power and refrigeration. Both first and second laws of thermodynamics were employed to develop a thermodynamic model, which has been applied to investigate the performance of combined cycle. Furthermore, performance of the combined cycle for ERC versus ARC was compared and assessed after altering operating parameters (turbocharger pressure ratio, turbocharger compressor efficiency, ambient temperature, and the entrainment ratio of ERC and generator temperature of ARC) to study their effect on engine power output, refrigeration load, exergy of refrigeration, and energy and exergy efficiencies of the cooling-power cogeneration cycle. Results show that the elevated pressure of turbocharger results in the enhancement of HCCI engine power and increase of the refrigeration of thermal load, simultaneously. However, the increasing ambient temperature shows the decline of HCCI engine efficiencies and energy efficiency of cogeneration, while the cogeneration cycle exergy efficiency is found increasing. Furthermore, the results are reported for the refrigeration performed by lithium bromide–water (LiBr–H2O)-operated ARC, and R134a- and R290-operated ERC, respectively. Mapping of exergy destruction for the presented cogeneration cycle discovered HCCI engine, boiler of ERC, generator of ARC, and catalytic convertor as the components of significant exergy destruction. Entrainment ratio and type of refrigerant employed in ERC and the generator temperature of ARC show a marginal impact on the COPs of these cycles.

Experimental investigation on the combustion and emissions in a pilot ignited direct injection natural gas engine using HCDI strategy

Pilot ignited direct injection natural gas engines have been increasingly attractive owing to their advantages in thermal efficiency and emissions. For conventional pilot ignited direct injection natural gas engines, soot emissions have been considered as an urgent issue, which could be possibly resolved by the adoption of homogenous charge direct injection strategy. To prove this viewpoint, this paper experimentally studied the effects of homogenous charge direct injection strategy on the combustion, emissions, thermal efficiency and operation stability of a pilot ignited direct natural gas engine. The results indicated that at low load, the application of homogenous charge direct injection strategies has negative effects on NOx, CO and HC emissions; though soot emissions could be improved, the negative effects seem to be more predominant. At high load, though NOx and HC emissions are impaired with the application of homogenous charge direct injection strategies, CO and soot emissions could be substantially improved with optimized injection parameters. Thermal efficiency could be slightly improved at low load condition and could be greatly raised at high load condition. Additionally, the adoption of homogenous charge direct injection strategies would increase the instabilities of engine operation, however, this behavior is more significant at low load condition.

Study of the Combustion Process of a Homogeneous Charge Compression Ignition (HCCI) Engine and a Partially Premixed Combustion (PPC) Mode of a Compression Ignition Engine Using Natural Gas as an Alternative Fuel

In order to investigate a viable approach to achieving high efficiencies and low nitrogen oxide (NOX) emissions, this paper presents the application of a homogeneous charge compression ignition (HCCI) engine and the partially premixed combustion (PPC) mode applied to a heavy diesel engine. The effect of carbon dioxide (CO2) fraction on combustion parameters was analyzed and discussed in detail. For this purpose, on the one hand, ANSYS CHEMKIN-Pro software was used to perform simulations of a closed homogeneous reactor under conditions relevant to HCCI engines, and on the other hand, ANSYS-Fluent software was used by adding a CO2 fraction varying from 20% to 58% to methane fuel to study 2D flow simulation by applying a PPC combustion mode to predict the distribution of various output parameters such as in-cylinder temperature, in-cylinder pressure and emissions. In comparison with the two presented models, it was found that the HCCI engine showed a lower NOX level than the PPC mode and this was due to the lower in-cylinder temperature in the HCCI engine.

Reducing pressure oscillation in high-load HCCI combustion via air injection before compression

Pressure oscillation often occurs in high-load homogeneous charge compression ignition (HCCI) combustion, which is a challenge in the development of HCCI engines for automobiles. This work proposes a novel method of reducing the pressure oscillation in HCCI combustion at high loads. The proposed technique injects air into homogeneous mixtures before compression, thereby giving local fuel concentration gradient. The fuel concentration gradient is expected to suppress a rapid pressure rise, resulting in reduced pressure oscillation. High-load HCCI combustion was simulated via a rapid compression machine with a high compression ratio. Varying the period from air injection to compression, that is, the waiting time, controlled the magnitude of fuel concentration gradient. The pressure oscillation was quantified and evaluated via the knock intensity (KI) and the averaged pressure rise rate. For the short waiting time; in other words, when the local fuel concentration gradient was large, the KI was very lower than that for no air injection. The KI, however, increased with the waiting time to approach that for no air injection. The oscillation modes were also different with and without air injection according to a modal analysis. The in-cylinder temperature distribution was visualized via the infrared radiometry to better understand the effect of air injection. For no air injection, the temperature in the cylinder uniformly increased, and the whole mixtures were ignited instantaneously. With air injection and for the short waiting time, on the other hand, hot spots developed on the rim of the injected air where the specific heat ratio was higher and then gradually spread throughout the chamber. Therefore, retarded auto-ignition and subsequently slow spread would limit a rapid pressure rise, resulting in reduced pressure oscillation in HCCI combustion. In conclusion, the proposed technique is effective for reducing the pressure oscillation in high-load HCCI combustion only for the short waiting time.

Comparative study of energy losses related to the ring pack operation in homogeneous charge compression ignition and spark ignition combustion

Low-temperature combustion in homogeneous charge compression ignition (HCCI) engine is one of the most promising technologies allowing to meet future emission targets for internal combustion engines. Whereas majority of research is centred on combustion itself, this paper for the first time points out the piston's energy losses induced by friction and blow-by in HCCI engine with negative valve overlap. The energy losses for HCCI and spark ignition (SI) operating modes were compared and thoroughly analysed with the use of the ring pack model. The input data for the simulations came from measurements made on a single-cylinder research engine capable of dual-mode combustion. The energy losses associated with friction of the rings against the cylinder varied from 8.2% of the indicated energy at the lowest load to 2.2% at the highest load tested, and were higher than in the SI mode by approximately 7%. The losses due to the gas leakage through the ring pack in the HCCI mode varied from 8% to 3.3%, respectively, and these losses were about twice as high as in the SI engine. The results demonstrated that energy losses due to blow-by are comparable with the friction losses of the rings, which are usually regarded as the prime source of inefficiency.

Thermodynamic and statistical analysis on the effect of exhaust gas recirculation on waste heat recovery from homogeneous charge compression ignition engines

Thermodynamic and statistical analysis on the effect of exhaust gas recirculation on waste heat recovery from homogeneous charge compression ignition engines

Lipschitz discrete observer design for HCCI engine mixed gas temperature at intake valve closed

The gas temperature for Homogeneous Charge Compression Ignition engine at intake valve closed is difficult to measure; so a Lipschitz discrete observer is designed. In particular, a single cylinder engine model is proposed. And, a thermodynamic process based state equation is presented considering the heat loss of residual exhaust gas. Consequently, a discrete nonlinear state observer is designed using Lipschitz condition. Finally, the numerical experiments are performed. The results demonstrate the effectiveness of the proposed observer in terms of the accuracy and robustness.

System for analysis and correction of motor management

The innovative system, which was developed for analysis and correction of motor management, is determined for the solution of practical problems concerning the operation of the piston combustion engines. Programming of the ignition curves and fuel maps without relevant feedback, namely, without information obtained from the engine operation, increases the risk of detonation combustion, which can destroy the combustion engine. However, the main application area of this system is the development of an algorithm, which is specified for control of the combustion process based on the HCCI technology (Homogenous Charge Compression Ignition). Nowadays, the functional principle of the HCCI engine is one of the most effective possibilities on how to reach higher operational efficiency of the gasoline engine, that is, closer to the efficiency level of the diesel driving units.

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.

Surface-modified elastomeric nanofluidic devices for single nanoparticle trapping

Our work focuses on the development of simpler and effective production of nanofluidic devices for high-throughput charged single nanoparticle trapping in an aqueous environment. Single nanoparticle confinement using electrostatic trapping has been an effective approach to study the fundamental properties of charged molecules under a controlled aqueous environment. Conventionally, geometry-induced electrostatic trapping devices are fabricated using SiOx-based substrates and comprise nanochannels imbedded with nanoindentations such as nanopockets, nanoslits and nanogrids. These geometry-induced electrostatic trapping devices can only trap negatively charged particles, and therefore, to trap positively charged particles, modification of the device surface is required. However, the surface modification process of a nanofluidic device is cumbersome and time consuming. Therefore, here, we present a novel approach for the development of surface-modified geometry-induced electrostatic trapping devices that reduces the surface modification time from nearly 5 days to just a few hours. We utilized polydimethylsiloxane for the development of a surface-modified geometry-induced electrostatic trapping device. To demonstrate the device efficiency and success of the surface modification procedure, a comparison study between a PDMS-based geometry-induced electrostatic trapping device and the surface-modified polydimethylsiloxane-based device was performed. The device surface was modified with two layers of polyelectrolytes (1: poly(ethyleneimine) and 2: poly(styrenesulfonate)), which led to an overall negatively charged surface. Our experiments revealed the presence of a homogeneous surface charge density inside the fluidic devices and equivalent trapping strengths for the surface-modified and native polydimethylsiloxane-based geometry-induced electrostatic trapping devices. This work paves the way towards broader use of geometry-induced electrostatic trapping devices in the fields of biosensing, disease diagnosis, molecular analysis, fluid quality control and pathogen detection.

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.

A Transported Livengood–Wu Integral Model for Knock Prediction in Computational Fluid Dynamics Simulation

Abstract This work describes the development of a transported Livengood–Wu (L–W) integral model for computational fluid dynamics (CFD) simulation to predict autoignition and engine knock tendency. The currently employed L–W integral model considers both single-stage and two-stage ignition processes, thus can be generally applied to different fuels such as paraffin, olefin, aromatics, and alcohol. The model implementation is first validated in simulations of homogeneous charge compression ignition (HCCI) combustion for three different fuels, showing good accuracy in prediction of autoignition timing for fuels with either single-stage or two-stage ignition characteristics. Then, the L–W integral model is coupled with G-equation model to indicate end-gas autoignition and knock tendency in CFD simulations of a direct-injection spark-ignition engine. This modeling approach is about 10 times more efficient than the ones that based on detailed chemistry calculation and pressure oscillation analysis. Two fuels with same Research Octane Number (RON) but different octane sensitivity are studied, namely, Co-Optima alkylate and Co-Optima E30. Feed-forward neural network model in conjunction with multivariable minimization technique is used to generate fuel surrogates with targets of matched RON, octane sensitivity, and ethanol content. The CFD model is validated against experimental data in terms of pressure traces and heat release rate for both fuels under a wide range of operating conditions. The knock tendency—indicated by the fuel energy contained in the autoignited region—of the two fuels at different load conditions correlates well with the experimental results and the fuel octane sensitivity, implying the current knock modeling approach can capture the octane sensitivity effect and can be applied to further investigation on composition of octane sensitivity.

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.