Homogeneous Charge Compression Ignition Research Articles

Effects of multiple fuel injection schedules and LPG energy share on combustion stability and output characteristics of dual-fuel HCCI engine

Homogeneous Charge Compression Ignition (HCCI) engine is a prominent solution to satisfy the stringent NOx emission norms. The current study investigates the influence of fuel injection strategies and LPG energy share on dual fuel powered HCCI engine at 1.8 bar and 3.6 bar BMEP at constant speed (2700 rpm) and injection pressure (50 MPa). Over the study D + LPO used as primary fuel and LPG as secondary fuel. The fuel injection strategies alike single, double, as well multi-pulse modes are studied at injection timings of 90obTDC aimed at single-pulse, 120°& 90°bTDC for double-pulse, 120°, 90°, & 30°bTDC for multi-pulse modes. All single, double, and multi-pulse injection modes at 0% LPG energy share obtains greater combustion rate and advanced combustion phasing. Further increase in LPG energy share, the rate of combustion is lessened and retarded toward TDC, consequently it enhanced the performance and emission characteristics of an HCCI engine. The optimum LPG energy share for single-pulse, double-pulse, and multi-pulse injections modes are 46.80%, 63.25%, and 78.06% respectively for 1.8 bar BMEP. For 3.6 bar BMEP optimum LPG energy shares are found to be 41.79%, 58.55%, and 71.76% for single, double, and multi-pulse injection respectively.

Development of a reduced chemical mechanism for ammonia/n-heptane blends

A reduced chemical mechanism for ammonia/n-heptane blends, which consists of 495 reactions and 74 species, is proposed in this study. This reduced mechanism is developed using the direct relation graph with error propagation (DRGEP) method based on the latest detailed kinetic mechanism of ammonia/n-heptane blends, which includes the important interactive reactions between n-heptane and ammonia (n-C7H16 + NH2 <=> C7H15 + NH3). The reduced mechanism was first validated against experimental ignition delay times (IDTs) and laminar burning velocities (LBVs) for different ammonia/n-heptane blends and can capture well these data. Moreover, both the detailed and reduced mechanisms were used to simulate the combustion and emission characteristics of a homogeneous charge compression ignition (HCCI) engine fueled by different ammonia/n-heptane blends. The simulation results show that the predicted auto-ignition timings and peak pressure values of the reduced mechanism match reasonably well with those of the detailed mechanism for different ammonia/n-heptane blends. Also, the predicted time-history profiles of the important pollutants, including NO, NO2, N2O and HCN, show reasonably good agreement between the detailed and reduced mechanisms, and the maximum discrepancy of the peak concentration is within a factor of two. The important reaction pathways of pollutant formations at HCCI engine conditions are discussed in detail. Furthermore, the current reduced mechanism is also used to simulate the combustion process of an ammonia/diesel dual-fuel engine. Overall, the engine combustion phasing, peak pressure, and heat release can be well simulated using the current mechanism, and the computational efficiency is acceptable.

Ion Current Based Data Driven Control of HCCI - the Key to Improve Pressure Based Control Strategies?

Homogeneous charge compression ignition (HCCI) is a low-temperature combustion process that can both increase efficiency and reduce pollutant raw emissions. The process is highly dependent on low-temperature kinetics of the chemical reactions that lead to auto-ignition. Due to strong coupling of consecutive combustion cycles stable control of HCCI is a major challenge. Ion current sensors that detect ionization in the combustion chamber can provide information about chemical reactions taking place inside the cylinder. In contrast, model-based HCCI control strategies, which require accurate models that describe the current cylinder state, are often based only on the cylinder pressure. However, low-temperature chemical kinetics are not sufficiently taken into account by only using the cylinder pressure signal. Therefore, the main hypothesis of this paper is that HCCI strongly depends on the chemical state in the cylinder, which cannot be adequately described by the pressure sensor in the cylinder alone. Hence, a conventional spark plug is used to apply an ion current sensor, which is used alongside the pressure sensor. The aim is to use further information about the state of the chemical mixture for the control of the engine. The features derived from the ion current are integrated into an explicit artificial neural network-based controller. The developed control strategies are then compared against a purely pressure-based controller. Using the ion current features, the standard deviation of the combustion phasing CA50 is reduced by up to 42% compared to the pressure-based approach. The experimental results of this work show that the inclusion of the ion current in the controller provides a significant advantage for low temperature combustion control.

Added value of thermodynamic white-box data for HCCI combustion prediction

Homogeneous charge compression ignition (HCCI) is a promising combustion process to reducing both greenhouse gas and pollutant emissions in the transportation sector. The combustion starts when the thermodynamic state of the cylinder charge reaches the auto-ignition properties of the fuel, which is challenging to model. In addition, the strong cyclic coupling due to required exhaust gas recirculation leads to a significant dependence on the combustion of the previous cycle.This work focuses on identifying accurate models to predict the combustion process for potential use in an MPC. In this work HCCI is achieved using negative valve overlap (NVO) on a fully flexible valve train. The fluctuating composition and temperature of the cylinder charge is not directly measurable and not taken into account in state of the art approaches. It is assumed that it has a decisive influence on the start of combustion. Hence, in this work, the thermodynamic state is modeled by a detailed physical white-box model, which is used as an additional input for the combustion prediction. To investigate the added value of the thermodynamic state data, an Artificial neural network (ANN) is trained to predict combustion both with and without the thermodynamic state data from the white-box model. The root-mean-square error of the ANN including thermodynamic data is reduced by 12.7%. Thus, by adding the thermodynamic white-box data, the HCCI combustion prediction can be significantly improved.

NOx Emissions of N-butanol and Methane in Low-speed Two Stroke Diesel Engines

This article firstly structures a detailed combustion reaction mechanism including methane N-butanol nitrogen oxide. According to two-stroke low-speed diesel engine’s parameter with the characteristics of engine firing, homogeneous charge compression ignition is selected as simulation model. At the same the output power and the excess air coefficient is 1.5, by means of the simulation calculation and analysis of reaction path and reaction mechanism, when N-butanol and methane are mixed in different proportions, the exhaust temperature in the reactor reduces with the increase of methane proportion in reactants. At the same time NO mole fraction increases with the proportion of CH4 in the mixed fuel decreases, but the NO2 mole fraction will increase with the proportion of CH4 in the mixed fuel increases.

A Review of Low Temperature Combustion Mode of Engine

Since the 21st century, people's increasing attention to fuel economy and environmental issues has prompted the engine research community to continuously develop new efficient and clean combustion theories and methods. In terms of combustion technology, many researchers have proposed different new engine combustion methods, such as homogeneous charge compression ignition combustion (HCCI), premixed charge compression combustion (PCCI), and reaction controlled compression ignition (RCCI), which are the three main low-temperature combustion methods. These combustion methods are different from the premixed combustion method of the spark ignition (SI) engine represented by the traditional gasoline engine and the diffusion combustion method of the compression ignition (CI) engine represented by the traditional diesel engine. The flame temperature affects the combustion and emission process of the engine, and realizes the efficient and clean combustion of the engine. This paper first briefly describes the conventional engine combustion method, and then briefly summarizes the comparison between these three low-temperature combustion methods and their respective combustion and emission characteristics as well as advantages and disadvantages, with respect to the conventional combustion method.

A Tabulated Chemistry Multi-Zone Combustion Model of HCCI Engines Supplied with Pure Fuel and Fuel Blends

Homogeneous charge compression ignition is considered a promising solution to face the increasing regulations imposed by the legislator in the transport sector, thanks to pollutant and CO2 emissions reduction. In this work, a quasi-dimensional multi-zone HCCI model integrated with 1D commercial software is developed and validated. It is based on the control mass Lagrangian approach and computes the mixture chemistry evolution through offline tabulation of chemical kinetics (tabulated kinetic of ignition). Thus, the simulation can predict mixture auto-ignition with reduced computational effort and high accuracy. Multi-zone schematization mimics the typical thermal stratification of HCCI engines, controlling the combustion evolution. The model is coupled to sub-models for pollutant emissions estimation. Initially, the tabulated chemistry approach is validated against a chemical kinetics solver applied to a constant-volume homogeneous reactor, considering various fuel blends. The model is then used to simulate the operations of four engines using different fuels (hydrogen, methane, n-heptane, and n-heptane/toluene/ethanol blend), under various boundary conditions. The model predictivity is demonstrated against pressure traces, heat release rate, and noxious emissions. The numerical results showed to adequately agree with measured counterparts (average relative error of 1.3% on in-cylinder pressure peak, average absolute error of 0.95 CAD on pressure peak angle, average relative error of 8.4% on uHCs emissions, absolute error below 1 ppm on NOx emissions) only adapting the thermal stratification to the engines under study. The methodology proved to be a reliable tool to investigate the operation of an HCCI engine, applicable in the development of new engine architecture.

Hydrogen production and separation in fuel-rich operated HCCI engine polygeneration systems: Exergoeconomic analysis and comparison between pressure swing adsorption and palladium membrane separation

Hydrogen is one of the most important base chemicals and discussed as a future energy carrier for power and heat generation, as well as energy storage. Producing hydrogen at low costs and low CO2 emissions is thus of increasing importance. This study addresses the thermodynamics and economics of hydrogen, power, and heat generation by partial oxidation of methane in fuel-rich operated homogeneous charge compression ignition (HCCI) engines. Therefore, a python model of two different process concepts with different hydrogen separation technologies was developed and analyzed: pressure swing adsorption (PSA) and palladium membrane separation. The operating conditions of the engine and the separation were evaluated by conducting a global sensitivity analysis. The most suitable engine operating parameters were found at an equivalence ratio of 2, an intake temperature of 200 °C, a rotational speed of 1500 1/min, and a compression ratio of 22. In direct comparison, PSA consistently yielded better results than the palladium membrane, and low feed pressures were favorable. Subsequently, the uncertainty of economic input values was investigated and the power and hydrogen costs evaluated. In the PSA case, the electricity and hydrogen costs were found in a range of 44.2 €/MWh to 97.6 €/MWh and 2.7 €/kg to 7.2 €/kg, respectively, with an overall exergetic efficiency of 68.3%. Therefore, the proposed polygeneration system provides electricity at competitive costs and hydrogen at costs similar to a small-scale steam reforming plant at comparable efficiencies. Further scaling up of the engine could provide hydrogen at the cost of large-scale steam reforming, making the proposed concept a promising alternative.

Optimization of homogeneous charge compression ignition combustion in a light-duty diesel engine operated using ethyl acetate-gasoline blends

The low temperature combustion mode of homogeneous charge compression ignition eliminates particulate matter and oxides of nitrogen (NO x) emissions trade-off that prevails in high-temperature, diffusion-controlled conventional diesel combustion (CDC). In the present research, the significant challenge of narrow operating load range that hinders the commercial implementation of light-duty HCCI engines was overcome by employing ethyl acetate-gasoline blends. The gasoline concentration in test fuels was reduced in 10% decrements, from 84% to 24%, to replace it with ethyl acetate. The use of ethyl acetate, a renewable fuel, can help solve the energy crisis due to the rapid depletion of fossil fuels. An ignition improver was blended in the test fuels in a predetermined amount of 6% so that combustion stability was not hampered at lower loads. Parametric investigations were conducted to study the effect of progressively increasing ethyl acetate in test fuels on HCCI combustion, performance, and emissions. The machine learning tool of artificial neural network was implemented to learn the behavior of the test engine, considering load and fuel composition as input variables. The feedforward artificial neural network models were developed to predict the start of combustion, combustion phasing, indicated thermal efficiency, and emissions of carbon monoxide, soot, NO x, and unburned hydrocarbon (HC). A multi-objective optimization was performed to arrive at the best operating condition by integrating artificial neural network models with the genetic algorithm. All the developed artificial neural network models could predict responses with acceptable accuracy. The genetic algorithm indicated that the optimum point of the operation was at 80% load and 65% ethyl acetate in the test fuels. Experiments were conducted to validate the optimal HCCI conditions that resulted in 27% higher indicated thermal efficiency, 54% lower HC+NOx, and 99% lower soot emissions than CDC. Overall, the present study demonstrated the benefits of considering ethyl acetate as a fuel to improve HCCI engine metrics of off-road diesel engines.

Water Vapor Blending Ratio Effects on Combustion Thermal Performance and Emission of Hydrogen Homogeneous Charge Compression Ignition

A numerical model of the micro-free-piston engine was developed and its correctness was verified by the comparison between the simulation and referential experiment results under the same work conditions. Based on this numerical model, the effects of the water vapor blending ratio (α) on combustion thermal performance and emission characteristics of hydrogen (H2) homogeneous charge compressing ignition (HCCI) were investigated numerically. The water vapor impact on combustion temperature was analyzed as well. The simulation results reveal that when the initial equivalent ratio is 0.5, blending H2 with water vapor can delay the ignition time and prolong the whole process. At the same time, the addition of water vapor to H2 decreases the peak combustion temperature and pressure, which will alleviate the detonation phenomenon of the combustion chamber. Moreover, the power output capacity and NOx emissions decrease with the increase in α. When α increases to 0.8, the mixture gas cannot be compressed to ignite. Finally, the dilution effect, thermal effect, and chemical effect of water vapor all have the potential to lower the combustion temperature and the dilution effect plays the leading role.

Experimental optimization of homogeneous charge compression ignition through fuel modifications and a relative comparison with reactivity controlled compression ignition

Reactivity controlled compression ignition (RCCI) and homogeneous charge compression ignition (HCCI) are suitable alternatives to improve the performance and emission metrics of conventional diesel combustion. Previous studies have shown that the gasoline/diesel RCCI outperforms diesel HCCI as it has a wider load range, higher brake thermal efficiency, and lower smoke and oxides of nitrogen emissions. The present work addressed the shortcomings of diesel HCCI by replacing diesel with low reactivity, high volatile methanol–gasoline blends. 2-ethylhexyl nitrate, an ignition quality improver, was added in small amounts (6 vol.%) to the blends to avoid misfiring, particularly at lower loads. There were two approaches to improve engine performance metrics of methanol–gasoline HCCI: exhaust gas recirculation and fuel composition variation. The best approach was chosen, and HCCI performed using the selected approach was compared with baseline RCCI. The methanol-gasoline HCCI was compared to baseline-optimized gasoline/diesel RCCI to demonstrate that the challenges associated with diesel HCCI can be overcome through fuel modifications. It was revealed that the strategy of varying methanol concentration in fuel blends was more effective than the strategy of varying EGR rate in terms of efficiency improvement and reduction of soot, carbon monoxide (CO) and unburned hydrocarbon (UHC) emissions. The parametric investigation showed that HCCI outperformed RCCI at mid to higher loads. For instance: at 60% load (3.19 BMEP), indicated thermal efficiency decreased by 7%, specific CO, UHC, nitrogen oxides, and smoke emissions elevated by 1.3, 1.2, 2.5, and 20.5 times for baseline-optimized RCCI than 40% methanol/54% gasoline/6% 2-EHN HCCI. Also, increased methanol in fuel during HCCI improved indicated thermal efficiency at a particular load. For instance, at 60% load, the indicated thermal efficiency improved by 30% during HCCI of fuel containing 40% methanol than 20% methanol. Overall, the present work discusses a practical method to efficiently use renewable methanol fuel in HCCI engines.

Numerical Simulation of HCCI Combustion Fuelled with Gasoline + Methyl Tert-Butyl Ether Blend

Background: Homogeneously charged compression ignition (HCCI) engines are generally popular for low production of NOx and Soot formation, also consuming lower fuel as compared with conventional gasoline and diesel engine. Objectives: In this study, the compression ignition engine (CI) was simulated in HCCI mode fuelled with Gasoline and Methyl tert-butyl ether (MTBE) blends, and the analysis was carried out in similar operating conditions as experimentation carried out. Methods: The chamber pressure was maintained at 2 bar, and the air-fuel ratio was maintained at2.75. The optimal blend for MTBE was fixed as 15 vol % (MTBE 15), and the measured properties of the blends were used in the simulation. ICE simulation module in ANSYS WORKBENCH was used for this current simulation. Both cold flow and combustion simulations were carried out and the results indicate velocity indie the cylinder, cylinder pressure, and temperature distributions for two cases such as gasoline and gasoline with MTBE15. Findings: The average velocity was found high with the MTBE blend, whereas in-cylinder pressure was found low with MTBE blend than with gasoline. The temperature inside the cylinder pressure was found higher with gasoline than MTBE blend. The deviation between the experimentation and simulation was found low. Novelty: The simulation provides a better understanding of the combustion phenomena when gasoline is mixed with MTBE and utilized in a diesel engine at HCCI mode. Keywords: CFD; MTBE; Gasoline; HCCI; Emission reduction

Optimizing the effect of a mixture of light naphtha, diesel and gasoline fuels on engine performance and emission values on an HCCI engine

In this study, the effects of using naphtha-diesel and naphtha-gasoline fuel mixtures were investigated using experimental and statistical methods on homogeneous charge compression ignition (HCCI) engine performance and emission values. Response Surface Method (RSM) was used as a statistical method. Fifty-two experiments were specified in the experimental set created by the RSM central composite design method, which were carried out under the same conditions. As a result of the experimental study, effective torque, brake-specific fuel consumption (BSFC), CO, HC, and NO emissions values were examined. The experimental results extrapolation equations were obtained with the RSM method, and the contour graphs were drawn. Optimum input parameters were determined to obtain the targeted output parameters. After the optimization, it was seen that the usage of gasoline fuel gave better results than diesel. Among the optimum input parameters, the gasoline ratio was determined as 0.297 %, the injection duration was 11.97 ms, and the engine speed was 1325.21 rpm. Effective torque was 12.79 Nm, BSFC value was 589.79 g/kWh, CO emission value was 0.11 %, HC emission value was 519.86 ppm, and NO emission value was 0 ppm depending on the optimum input parameters.

Experimental study of homogeneous charge compression ignition combustion in a light-duty diesel engine fueled with isopropanol–gasoline blends

Homogeneous charge compression ignition (HCCI) is a high-efficiency, ultra-low emission generating combustion technique that can potentially phase out conventional diesel combustion (CDC). Due to wide misfire and knocking limits, a limited load range impedes its commercial success. The present work addresses HCCI limitations using isopropanol–gasoline blends in a port fuel injected light-duty diesel engine. A cetane booster additive, 2-ethylhexyl nitrate (2-EHN), at 5vol.% was mixed with the test fuels to broaden the HCCI lower load limits. The tested fuels include biofuel isopropanol that replaced non-renewable gasoline in 20% increments to achieve higher loads during HCCI. The results show a substantial increment in HCCI operating load range (24%–86%) with test fuels over diesel HCCI (20%–38%). The characteristics of HCCI combustion in the modified test engine were benchmarked with CDC in the unmodified production engine. The significant benefits of HCCI over CDC were the concomitant reduction of indicated specific energy consumption (ISEC), oxides of nitrogen (NOx), and soot emissions, especially at higher loads. For instance, at 80% load, the ISEC, soot, and NOx were decreased by 5%, 99%, and 77%, respectively, for 60% isopropanol/35% gasoline/5% 2-EHN fueled HCCI than CDC. The exergy analysis was conducted to gain insight into irreversibility sources in thermodynamic processes during HCCI and CDC. The second law efficiency of HCCI improved with increased isopropanol content in the test fuels at a specific load. Overall, the present work shows that isopropanol–gasoline blends are viable alternatives to diesel to operate the HCCI engine that meets the desired emission and performance targets.

Utilization of multiwalled carbon nanotubes (MWCNT) additive in HCCI engine to widen operating range

Homogenous charge compression ignition (HCCI) combustion mode is a promising technology for the future of internal combustion engines because of its high thermal efficiency. However, HCCI engines have limited stable operating range which is a major drawback. Nanoparticles usage as fuel additive provides improvement of combustion characteristics of internal combustion engines. The objective of this study is to enlarge operating range of HCCI engine. For this purpose, the effects of multiwalled carbon nanotubes (MWCNT) on combustion characteristics of an HCCI engine were scrutinized. The effects of MWCNT on engine operating range, combustion parameters, and HC and CO emissions were determined. The maximum operating range was obtained with 75 % n-heptane, 25 % ethanol, and 100 ppm MWCNT mixture. Compared to 75 % n-heptane and 25 % ethanol mixture, 75 % n-heptane, 25 % ethanol, and 100 ppm MWCNT mixture increased the operating range of engine 112 %. Furthermore, in-cylinder pressure, heat release rate, indicated thermal efficiency, and maximum pressure rise rate were increased with use of MWCNT additive. Start of combustion and 50 % heat release location was shifted to earlier crank angles. Combustion duration was shortened. HC and CO emissions were also decreased.

Strategies to achieve controlled auto-ignition (CAI) combustion: A review

Conventional gasoline engines suffer from low performance and NOx emissions. Controlled auto-ignition (CAI), sometimes referred to as homogeneous charge compression ignition (HCCI), is a promising concept to solve such problems. CAI has the potential to improve spark ignition (SI) engine fuel economy while at the same time solving the trade-off of NOx-soot emissions found in compression ignition (CI) engines. The CAI engine can reach a fuel economy comparable to that of a conventional diesel engine with ultra-low NOx and negligible soot emissions. However, controlling auto-ignition remains the biggest difficulty that hinders the implementation of CAI as a commercial engine. Research towards a cleaner and more efficient engine is driven by the progressively stringent emission regulation imposed worldwide. Therefore, the CAI was developed to meet the emissions target while maintaining engine performance. CAI works on the principle of lean mixture and auto-ignition. To obtain CAI combustion, the temperatures in the cylinder must be sufficient to initiate auto-ignition. Without the use of a spark plug or injector, the CAI suffers from a direct control mechanism to start the combustion. The most practical approach to controlling the initiation of auto-ignition in CAI is diluting the intake charge by either trapping the residual gas or recirculating the exhaust gas. Both approaches enable the engine to achieve CAI combustion without requiring significant modifications to control the onset of CAI combustion phase.

Current status and prospect of homogeneous charge compression ignition (HCCI) technology application of transportation

HCCI engine is a new concept in recent decades. HCCI is defined as a type of engine with little application and market proportion. HCCI engines have great potential and prospects in practical engineering applications. However, there is a lack of cognition of HCCI engine development. Therefore, this paper introduces the current status of HCCI technology application and the possible development in the future. Throughout collecting information of some parameters of engines and comparison and analysis, this paper researches the current status and prospect of HCCI engine application. Research shows that, HCCI engine has considerable merits, which are more eco-friendly, higher thermal efficiency and fuel economy, also HCCI engine is not be used in production. In the future, HCCI engine will expand the advantages and occupy market, eventually be the mainstream type of internal combustion engine. In addition, the analysis and research results of this paper will provide reference and reference for the future development of HCCI engine.

Exergy analysis and investigation on effect of inlet valve closing temperature and hydrogen enrichment in syngas composition in an HCCI engine

This study presents the parametric investigation of syngas fuelled homogeneous charge compression ignition (HCCI) engine. The chemical kinetic simulation of the syngas HCCI engine is performed using the stochastic reactor model (SRM). This study first compares and evaluates the performance of different reaction mechanisms for the HCCI engine. The experimental combustion pressure data is compared with numerically investigated combustion pressure to validate the reaction mechanisms. Results indicate that a numerically simulated combustion pressure using a detailed reaction mechanism consisting of 173 reactions and 32 species (CRECK-2014) is well-matched with the profile of experimental combustion pressure. The validated reaction mechanism is further used to investigate the HCCI engine at different engine speeds for various equivalence ratio (ϕ), syngas composition (hydrogen addition (H2:CO)) and inlet valve closing temperature (Tivc). The sensitivity analysis is performed to find the prominent reactions in the oxidation reaction mechanism. Based on the combustion characteristics, syngas HCCI maps are developed. The effect of engine operating conditions on combustion and emission characteristics is also investigated. Furthermore, the result of engine operating parameters on converting fuel energy into physical exergy, chemical exergy, work exergy, and heat loss exergy is also briefly discussed.

Experimental investigation on diesel ignited dual fuel homogeneous charge compression ignition engine for the selection of suitable alcohol based fuel

Homogeneous charge compression ignition (HCCI) engine has fuel flexibility and can reduce NOX and soot emissions. The present work aims to investigate the dual-fuel mode HCCI engine (DF–HCCI–E) performance and exhaust emissions for different fuel types, namely, Methanol, Ethanol, Propanol, and Butanol. The CI Engine is converted into a DF-HCCI engine by attaching the carburetor to the inlet manifold for experimentation. Royal Enfield bullet 500 cc, Mikarb type carburetor was attached outside the engine cylinder to prepare the homogenous air-fuel mixture. Alcohol-based fuel (low reactivity) was supplied through the carburetor at the suction stroke time. Diesel (high reactivity fuel) was injected to start the combustion at the end of the compression stroke. It is observed that the P100+D DF–HCCI–E is suitable for low and high load conditions, while B100+D DF–HCCI–E is suitable for mid-load conditions. Results showes that Methanol has the highest cooling potential and lowest NOX emission compared to the rest of the fuels. And also, B100+D DF–HCCI–E reduced the highest smoke opacity for all load conditions compared to the rest of the ABF. Simple Additive Weighting (SAW) optimization was carried out, and it is concluded that P100+D has the best cumulative performance for low and high load conditions and M100+D has the poorest cumulative performance for all load conditions.

Effects of natural-gas blending on ignition delay and pollutant emission of diesel fuel for the condition of homogenous charge compression ignition engine

• Effects of blending of natural gas (NG) with diesel fuel were investigated. • Major properties of diesel were measured at 40 bar and its surrogate fuel was formulated. • Blending of NG reduces pollutant emission with slight decrease in heat production. • Ignition timing is changed by NG blending, but, it is not significant. • The optimal mixture ratio of NG in the dual fuel is suggested in HCCI engines. Burning of dual fuel of diesel and natural gas is a promising technique in compression ignition engine in the aspects of fuel economy and reduced emission. Effects of blending of natural gas with diesel fuel are investigated numerically and experimentally with respect to ignition delay, heat production, and pollutant emission. First, major properties of diesel are measured at high pressure of 40 bar, which is an engine-relevant condition, and thereby, a surrogate fuel with higher accuracy is formulated, which has properties closer to diesel than the other existing surrogate fuels. Especially, as one of key properties, high molecular weight of diesel is considered critically in formulating a surrogate fuel. Ignition delay times of several mixtures of diesel and natural gas (NG), of which mixture ratios of 100/0%, 60/40%, and 20/80%, are measured by a shock tube in the ranges of temperature from 770 K to 1,000 K and of equivalence ratios from 0.5 to 2.0. Measured ignition delay is compared with that calculated by numerical simulations with the surrogate fuel formulated in this study for its validation. Finally, combustion simulations of HCCI (homogeneous charge compression ignition) are conducted with the mixture of diesel and NG and compared with available experimental data. And thereby, optimal mixture ratio of the dual fuel is suggested in terms of ignition time and pollutant emission acceptable in HCCI engines.