Homogeneous Charge Research Articles

HCCI combustion of methanol along with diesel through novel injection strategies and its potential over conventional dual fuel combustion

In this experimental work Homogenous Charge Compression Ignition of methanol along with direct injection of diesel (HCCI-DI) was achieved by adapting novel injection strategies for controlling the charge homogeneity and ensuring proper combustion in a single cylinder common rail water cooled research engine run at a constant speed of 1500 rpm. Methanol was port injected while the diesel was injected as two pulses – an early first pulse (during start of suction) for enhancing the charge homogeneity and a late second pulse for controlling ignition. The effects of methanol energy share (MES), start of injection of the first and second pulses (SOI-F and SOI-S) and first pulse injected quantity (FIQ) at different loads were studied. The SOI-S of diesel had to be advanced with load for best thermal efficiency. At full load, it had to be retarded to limit knocking. Heat release analysis indicated that higher FIQs resulted in slow combustion as the charge was more homogeneous while lower FIQs formed a stratified mixture that enhanced the thermal efficiency, reduced THC and unregulated emissions while elevating the NOx levels. The thermal efficiencies were higher by about 2.9 and 1.9% compared to the Conventional Dual Fuel (CDF) operation at 75% and 50% loads. The MES that could be tolerated was higher than the CDF mode. Soot was significantly reduced as compared to the CDF mode by 94%, 87.6%, 80.3% while the NOx was reduced by 77.5%, 65.2% and 29.9% at the IMEPs of 5.1, 6.2 and 7.5 bar respectively. However, emissions of unburnt hydrocarbons, carbon mono-oxide, methanol and formaldehydes were higher than the CDF mode. On the whole the methanol diesel HCCI-DI mode has the potential for operation with higher efficiency, lower NOx and soot emissions than the CDF mode.

Combustion control of DME HCCI using charge dilution and spark assistance.

To realize the potential of DME for clean combustion, fueling control is essential. In this research, the challenges, advantages, and applicability of high-pressure direct injection and low-pressure port injection are reviewed and evaluated, especially in relevance to HCCI combustion. In this study, emphasis is given to the applicable ranges of low-pressure fuel delivery in relevance to load, air-fuel ratio, and inert gas dilution, for realizing HCCI combustion. The strategy of high-pressure direct injection is advantageous for combustion phasing control, but the fuel handling is challenging because of the high vapor pressure of DME fuel. The strategy of port fuel injection is prone to early combustion and, consequently, tends to produce excessive pressure rise rates in the combustion chamber. This challenge is escalated at higher engine loads, making homogenous charge compression ignition difficult to achieve. In this paper, the load extension of DME-fueled HCCI combustion was explored. First, the impact of dilution on the combustion characteristics of DME HCCI was studied under lean and CO2 diluted conditions. Under the present empirical setups, results show that the lean-burn strategy has limited capability of combustion phasing control, especially when the engine load is above 5 bar IMEP. The CO2 dilution strategy can significantly retard the combustion phasing until the fulfillment of combustion becomes unstable. It was found that spark assistance is advantageous for combustion control. With an effective application of excess air, intake CO2 dilution and spark assistance, an engine load of 8 bar IMEP was reached with appropriate combustion phasing, with ultra-low NOx emissions.

Numerical assessment of interchangeability potential for syngas-fueled rotary engine

The syngas-fueled rotary engine can be considered as a promising solution for small–scale decentralized power generation due to high specific power, engine simplicity, smoothness and a low tendency for abnormal combustion. Since the decisive feature of syngas refers to feedstock flexibility, in this study we consider syngas with various compositions, produced from biomass, coal and natural gas, as a primary fuel for rotary engines. It was shown that rotary engine performance, efficiency and emission are mostly affected by the balance between combustion promoters and diluents in the air-syngas mixture. Particularly, high hydrogen concentration and lower inert content result in maximum power, heat release and thermal efficiency for stoichiometric and lean conditions. For the rotary engine with a homogeneous charge of the fuel, the combustion process is characterized by the weak influence of turbulence, while the laminar flame speed is an influential parameter in combustion behavior. The high magnitude of specific fuel consumption makes it difficult for engine operation at lean conditions. Although, the lean mixture cannot provide enough high flame temperature for NOx formation. The CO2 emission is affected by the hydrogen to carbon ratio. The opposite trend is observed between NOx and CO emission pathways due to oxygen availability. The power generation system based on the syngas-fueled rotary engine with syngas produced by not only well-known technology such as gasification or steam reforming but novel concepts (non-catalytic partial oxidation) can provide sustainability to the energy sector and reduce consumption of fossil fuels..

Simulation Research of the n-Butanol Proportion Influence on HCCI Combustion of Free-Piston Diesel Engine Generators

For researching the influence of n-butanol proportion in diesel fuel on homogeneous charge compression ignition (HCCI) combustion of the free-piston diesel engine generator (FPDEG), a three-dimensional (3D) moving mesh computational fluid dynamics (CFD) simulation model of a FPDEG prototype was developed. A detailed chemical reaction mechanism of diesel fuel was selected as the HCCI combustion mechanism and coupled in the established HCCI combustion simulation model of the FPDEG prototype. The validity of the established HCCI combustion simulation model is proved by comparing the simulation and experimental pressure curves under the condition of pure diesel fuel. The simulation results of different n-butanol proportions in diesel fuel showed that as the n-butanol proportion increased from 0 to 60%, the maximum heat release rate decreased to 59.6 J/deg, the calculated indicated thermal efficiency augmented to 4.6%, the calculated indicated mean effective pressure increased to 0.057 MPa, and the final NOx and CO content decreased to 0.239 and 0.57 g/kg fuel, respectively, but the final soot content increased to 0.000562 g/kg fuel. Therefore, the n-butanol proportion of diesel fuel played a vital role in combustion and emission progress of the FPDEG.

Effect of mixture formation mode on the combustion and emission characteristics in a hydrogen direct-injection engine under different load conditions

Significant efforts are currently underway to transform the transportation industry from a fossil fuel-based industry to a hydrogen-based industry to achieve the goal of zero carbon emissions. In this study, hydrogen direct injection (DI) is implemented using three mixture formation modes: homogeneous charge, lean-homogeneous charge, and lean-stratified charge (LSC). The main objective is understanding the effect of the hydrogen mixture mode on the efficiency and emission characteristics of the hydrogen DI engine. Accordingly, hydrogen was used as the fuel in a spray-guided single-cylinder research engine. The results revealed that owing to the high heat loss characteristics of hydrogen, the optimized combustion phasing angle was retarded. The LSC mode minimized heat transfer loss by reducing the high-temperature area near the cold cylinder wall. Furthermore, it had the highest indicated thermal efficiency (ITE) of 34.09 %, especially under low load conditions. However, the stratified rich hydrogen in the LSC mode resulted in high nitrogen oxide emissions (6.68 g/kWh). Heat management is vital to efficiently extract energy from hydrogen in an internal combustion engine. Heat loss reduction (13 %) contributes more to high ITE than pumping loss improvement (2 %) in the LSC mode.

The Start of Combustion Prediction for Methane-Fueled HCCI Engines: Traditional vs. Machine Learning Methods

In this work, 11 regression models based on machine learning techniques were employed to provide a fast-response and accurate model for the prediction of the start of combustion in homogeneous charge compression ignition engines fueled with methane. These regression models are categorized into linear and nonlinear types. Although the robust random sample consensus (RANSAC) model is a nonlinear type as well as SAM (simple algebraic model), the prediction accuracy is enhanced from 89.3% to 98.4%. Such accuracy is also achieved for the linear models, namely, ordinary least squares, ridge, and Bayesian ridge models. Indeed, due to the linear hypothesis (the correlation for the start of combustion prediction), the presented models have an acceptable response time to be used in real-time control applications like the electronic control units of the engines.

Enhancement of mixture homogeneity for DI-CI engine to achieve Homogeneous Charge Compression Ignition (HCCI) combustion characteristics: a numerical approach

ABSTRACT Homogeneous Charge Compression Ignition (HCCI) engine is a new mode of engine combustion concept used for decreasing emissions like NOx and soot and to meet stringent emission norms. A numerical and modeling analysis of the performance and emission characteristics of a DI-CI engine is presented in this paper. The numerical analysis was carried out using CONVERGE CFD software. In this paper, four different engine parameters were considered, i.e., Compression Ratio (CR) (14.5 to 19.5), Exhaust Gas Recirculation (EGR) (0 to 30%), Fuel Injection Pressure (FIP) (200 to 280 bar), and Start of Injection (SOI) (17 to 29° CA bTDC). Response Surface Methodology (RSM) was used for developing the design matrix in the given parameter ranges. Results were analyzed in terms of NOx, soot emissions, and Indicated Specific Fuel Consumption (ISFC) with an objective of lowering ISFC, soot, and NOx. The statistical analysis showed that CR of 18.9, SOI of 25.89° CA bTDC, EGR of 24.9%, and FIP of 262.45 bar predicted as an optimum combination of operation parameters set. From the ANOVA analysis, it is observed that CR and SOI are the most influencing parameters on the output response parameters. The mixture homogeneity (i.e., Target Fuel Distribution Index (TFDI)) of air-fuel was improved by 19.2% for optimum configuration as compared to baseline configuration.

Low-Temperature Oxidation of Di-n-Butyl Ether in a Motored Homogeneous Charge Compression Ignition (HCCI) Engine: Comparison of Characteristic Products with RCM and JSR Speciation by Orbitrap

Low-Temperature Oxidation of Di-<i>n</i>-Butyl Ether in a Motored Homogeneous Charge Compression Ignition (HCCI) Engine: Comparison of Characteristic Products with RCM and JSR Speciation by Orbitrap

Application of machine learning to optimize the combustion characteristics of RCCI engine over wide load range

The objective of this study is to investigate, optimize, and compare the combustion features and intake variables affecting the kinetics of gasoline/diesel RCCI engine by applying the genetic algorithm. Six decision variables include the fuel flow rate (FFR), premixed fuel rate (PFR), exhaust gas recirculation (EGR) rate, first injection mass ratio (IMR1), and the first and the second start of injection (SOI1 and SOI2). The objective of the optimization was to simultaneously maximize the engine gross indicated efficiency (GIE), the second law efficiency (SLE), and minimize exhaust emissions and the maximum pressure rise rate. The optimal space filling design of experiment method was applied to evaluate the effect of the decision variables on the objective functions with a minimum number of numerical experiments. The relationships between the decision variables and objective functions were approximated by the genetic aggregation response surface model. Finally, the non-dominated sorting genetic algorithm II was employed to find the optimum values. In the optimal case GIE, SLE, and Fmerit increased by 1.56%, 1.25%, and 15.14% while NOx concentration and engine noise reduced by 16.67% and 33.45%, respectively. The best range of SOI2 for GIE is between –22 and −14 degrees ATDC, while for improving SLE, SOI2 should be advance. Sensitivity analysis shows that PFR and FFR are the most influential variables to moderate the combustion kinetics and increasing IMR1 has the proper effect on combustion by creating more opportunities for a homogeneous charge and reducing hot spots.

A comparative study of PODE/gasoline and n-heptane/gasoline in a spark-assisted homogeneous charge compression ignition engine with dual-injection strategies and EGR

Homogeneous charge compression ignition (HCCI) has potential to improve thermal efficiency for gasoline engine due to the similar formation of mixture between HCCI and traditional spark ignition mode. High reactivity fuel combined with gasoline is used to achieve HCCI combustion with a relative low compression ratio. Polyoxymethylene dimethyl ethers (PODE) is a kind of low-carbon fuels with unique molecule structure, which is beneficial for carbon neutral. The intermediate products of PODE are different from those of long-chain alkane such as n-heptane and diesel. In this paper, the difference in spark-assisted HCCI (SA-HCCI) combustion combined with spark ignition and EGR between PODE/gasoline and n-heptane/gasoline under different operating conditions were investigated. The results illustrated that PODE/gasoline was more suitable for SA-HCCI combustion due to the positive relation between thermal efficiency and gasoline percentage, which can significantly improve the thermal efficiency while suppressing knock. Although the cetane number of PODE is greater than the n-heptane, the SA-HCCI combustion was more violent fueled with n-heptane/gasoline than that of PODE/gasoline. Low NOx and PM emissions are achieved for SA-HCCI combustion especially for PODE/gasoline. The advancing spark timing reduced the incomplete combustion and shortened the combustion duration, thus reducing the THC and CO emissions, especially fueled with PODE/gasoline. Although a low EGR rate can slightly improve the THC and CO emissions, violent combustion can be significantly improved. In general, high efficiency and low emissions could be achieved by PODE/gasoline and spark ignition combined with EGR. The brake thermal efficiency for SA-HCCI combustion fueled with PODE/gasoline increased by 30% compared with DISI mode under the same loads.

Study on the ignitability of a high-pressure direct-injected methane jet using a scavenged pre-chamber under a wide range of conditions

Natural gas is a promising alternative fuel for internal combustion engines, it allows for a reduction of engine-out emissions without impairing high engine efficiencies. Although this approach is already utilized from small to large engine classes, it is almost exclusively based on the combustion of a premixed homogeneous charge. For ignition, small engines use standard spark plugs or pre-chambers, while large and lean-operated engines use pre-chambers and pilot injections. Direct high-pressure gas injection is a more recent, alternative way to operate gas engines which offers benefits compared to premixed operation such as high combustion pressures, leaner operation, easier quantity regulation, and higher compression ratios, among others. However, in contrast to diesel injection, the compression temperatures are too low for the auto-ignition of the gas jets. Therefore, an additional ignition system is required, usually a pilot injection system is used. In this study, the usability and performance of a scavenged pre-chamber used for the ignition a high-pressure gas jet has been investigated in an optically accessible test-rig that is able to operate at engine-like conditions. Results show that the turbulent hot jet generated by the pre-chamber was able to ignite the high-pressure gas jet under a wide range of operating conditions. Moreover, it also appears to be a promising ignition strategy for very early direct injection during the compression stroke as well as for port injection. The good performance is attributed to the intense mixing of the main gas jet with the hot jet exiting the pre-chamber.

Experimental investigation on effects of equivalence ratio on combustion with knock, performance, and emission characteristics of dimethyl ether fueled CRDI compression ignition engine under homogeneous charge compression ignition mode

This study deals with the effects of different equivalence ratios on combustion with a knock, performance, emissions of a DME fueled automotive CI engine under HCCI mode. The conventional common rail direct injection (CRDI) CI engine was modified to run with DME fuel (manifold injection) under HCCI mode. The experiments were conducted on the engine at different equivalence ratios at a constant speed of 1400 rpm. Two stages of combustion (low-temperature reaction (LTR) region and high-temperature reaction (HTR) region) were observed under HCCI mode. The LTR region occurs at the temperature range from 700 to 750 K. In contrast, the HTR region was at a temperature beyond 1000 K. The cyclic variations with the coefficient of variation (COV) of maximum in-cylinder pressure, indicated mean effective pressure with knock peak pressure and knocking intensity (KI) were analyzed for assessment of combustion stability. Based on the knocking intensity, the optimum equivalence ratio with controlled auto-ignition (CAI) was found as 0.55, with peak in-cylinder pressure of 70.87 bar and peak in-cylinder temperature of 1815 K. The COV for all the parameters and KI found below the limit value (COVlimit − 5% and knocklimit − 5 MW/m2) till 0.55 equivalence ratio and beyond the equivalence ratio, the knock occurred resulting in uncontrolled auto-ignition (UAI). Ultra-Low NOx (10–15 ppm) and zero smoke emissions with a considerable reduction in CO and HC emissions were observed at a higher equivalence ratio from DME fueled HCCI mode. However, CO and HC emissions were higher at lower equivalence ratio. This study shows that the simultaneous reduction of NOx and smoke emissions could be achieved in a DME fueled HCCI engine.

Syngas composition for improving thermal efficiency in boosted homogeneous charge compression ignition engines

Various syngas compositions were experimentally investigated in a homogeneous charge compression ignition (HCCI) engine to suggest an optimal composition that can maximize thermal efficiency. Intake boosting was also implemented to extend the high-load operating range over a wide range of equivalence ratios. The engine speed was selected as 1,800 rpm and the intake pressure was increased from 0.19 MPa to 0.26 MPa. The thermal efficiency improved by increasing the intake pressure, and incrementally increasing the equivalence ratio until the maximum pressure rise rate (MPRR) limit was reached. The increase in intake pressure also extended the engine load by increasing the syngas fuel input. The syngas composition was systematically varied to clarify the effects of H2 and CO contents on the combustion and emissions of the HCCI engine. H2 was increased from 30% to 50%, whereas the CO amount was reduced from 25% to 8% for maintaining a constant lower heating value (LHV). Although the intake temperature decreased with increasing the H2 content, the thermal efficiency improved. The increase in H2 content was more effective in enhancing combustion performance than the intake temperature reduction. The engine load also slightly increased owing to the improvement in the thermal efficiency. Furthermore, the CO emission also decreased. The NOX emissions remained low despite the enhanced combustion performance. The CO-absent fuel compositions were also evaluated to improve the thermal efficiency. The highest gross indicated thermal efficiency of 43.4% was recorded with a CO-absent fuel composition (50% H2 and 50% CO2). However, the achievable engine load reduced because the LHV was lower than that of CO-present syngas. In the case of CO-absent fuel compositions, it was difficult to operate the HCCI engine with an H2 content higher than 50% owing to its excessive MPRR. Therefore, a syngas composition with a high H2 content and a low CO content was favorable for high-load extension in the HCCI engine.

Numerical Investigations on Oxides of Nitrogen Mitigation Strategies in a Homogeneous Charge with Direct Injection Engine

Numerical Investigations on Oxides of Nitrogen Mitigation Strategies in a Homogeneous Charge with Direct Injection Engine

Numerical investigation of combustion characteristics of a single-cylinder linear engine fueled by natural gas under the influence of exhaust gas recirculation

The effect of applying the exhaust gas recirculation technique on the performance of a free-piston engine, including the resulting emissions, is introduced and assessed in this study. The simulation process has been performed over a single-cylinder, two-stroke free-piston engine that uses a homogeneous charge compression ignition. Two main sub-models that work implicitly to simulate the engine performance and emissions in an iterative simulation procedure using MATLAB® and Cantera toolbox. It was found that recycling a small percentage of the exhaust gases (∼10%) has a significant effect on reducing the engine emissions, like the NO x levels. Four different levels of EGR were applied in the simulations at , , and . Raising the percentage of the recirculated gases beyond a specific threshold will encounter a negative outcome by increasing the emissions of other particles, such as the UHC and CO. Moreover, it can lower the oxygen (O2) concentrations causing an incomplete fuel–air burning which reduces the combustion efficiency. The recirculation of 30% of the exhaust gases was aggressively able to reduce about 14 g/kWh of NO x at the ignition time compared to no recirculation, and about 8 g/kWh at the steady state.

Experimental Investigations of Injection and Combustion Parameters of a Homogeneous Charge Compression Ignition (HCCI) Engine with a Multi-Injection Common Rail System

This work experimentally investigates the most imperative parameters that control the injection and combustion processes in a multi-injection HCCI Diesel engine namely; fuel-line pressure, timing of multi-injection events and the resulting in-cylinder pressure. These parameters in addition to the heat release rates are evaluated at different engine loads and speeds over up to 42 successive cycles. The main inter-relations of these parameters are also discussed. Results revealed that the maximum cylinder pressure and temperature in the HCCI engines are lower by 7% compared to similar conventional ones, which could lead to lower NOx emission. In addition, the fuel line pressure exhibits nearly the same major frequency of the waves, 850 to 950 Hz. Those results could be very useful for engine assessment, modeling, control, NOx reduction and power saving.

Effect of boundary conditions and n-heptane on methyl decanoate HCCI combustion and emission based on two-stroke diesel engine

The initial boundary conditions, combustion, and emission characteristics of methyl decanoate (MD) mixed with different proportions of n-heptane (N-Hep) for homogeneous charge compression ignition (HCCI) are studied in this work. MAN B&amp;W 6S70MC two-stroke diesel engine was used as the engine model of the reactor. The results showed that, when the equivalence ratio is 0.48, the NO emissions in the MD and N-Hep HCCI combustion process decrease with the decrease of the initial temperature. The initial temperature is determined to be 380 K. At the same time, NO emissions decrease with the increase of initial pressure, and the initial pressure is determined to be 1.3 atm. The results also indicate that, at a certain initial temperature, the initial pressure and total mole fraction of fuel, CO2, NOx reaction rates, and emissions are reduced significantly with the increase of N-Hep percentage in MD and N-Hep mixing combustion.

Exergy analysis in a HCCI engine operated with diethyl ether-fusel oil blends

Homogeneous Charge compression ignition (HCCI) combustion mode is a very interesting new combustion model with high efficiency, low nitrogen oxide (NOx), and soot emissions. In the present investigation, the performance of an HCCI engine operated with three fuel ratios, i.e., 40% diethyl ether and 60% fusel oil (D40F60), 60% diethyl ether and 40% fusel oil (D60F40), and 80% diethyl ether and 20% fusel oil (D80F20), at different lambda values and engine speeds was assessed from exergy indicators. The results indicate that the lambda variation allows observing the best performance zones when operating with fuel blends. From the comparison of the exergy indicators, it is concluded that the highest engine efficiency is obtained when operating with D40F60 at a lambda between 2.1 and 2.2. However, it was determined that the increase of diethyl ether in the blend decreases the HCCI engine performance. Also, greater stability of performance was recorded when operating with D80F20. A higher exergy destruction rate is observed between lambda 3.4 and 3.9 when operating with D80F20. The exergetic efficiency values varied from 5.34% to 23.85%. According to the results obtained, the lowest and highest value of exergy efficiency was recorded for the D80F20 and D40F60, respectively.

Physics-based modeling of homogeneous charge compression ignition engines with exhaust throttling

Homogeneous charge compression ignition (HCCI) engines create a more efficient power source for either stationary power generators or automotive applications. Due to the absence of direct actuation of ignition, HCCI based combustion control is quite challenging. For the purpose of control synthesis and design, a crank-angle based dynamic model of an HCCI engine with internal exhaust gas recirculation (EGR) is proposed in this paper. The HCCI autoignition timing is controlled by the amount of internal EGR induced by the cost effective exhaust throttling strategy. The zero dimensional single zone model is developed based on conservation of mass and energy and ideal gas law. The model is comprised of five subsystems: cylinder volume, intake, and exhaust runners along with combustion and heat-transfer models. Inputs to the model include engine speed, intake temperature, fueling rate, intake, and exhaust throttle positions. Outputs of the model contain the pressure, temperature, mass and burned gas fraction in the intake, exhaust and cylinder, air-to-fuel ratio (AFR), heat release rate, combustion phasing, and the indicated mean effective pressure (IMEP). The model is developed based on MATLAB/Simulink and validated against experimental data under steady-state and transient conditions at various intake temperatures, fueling levels, and exhaust throttle positions. Results demonstrate that by changing the exhaust throttle position, the pressure in the exhaust runner is regulated. As a result, the residual gas fraction is altered, leading to changes in mixture temperature and thus control of the HCCI combustion phasing. In the end, closed loop simulation is conducted with a linear quadratic Gaussian (LQG) controller applied to the crank-angle based model for regulation of combustion timing CA50 using exhaust throttle during load (fueling level) changes. In the future, this model can be utilized for control development and hardware in the loop (HIL) simulation.

Effects of variations in fuel properties on a homogeneous charge compression ignited light-duty diesel engine operated with gasoline-isobutanol blends

Homogeneous charge compression ignition (HCCI) is a promising alternative combustion mode to conventional diesel combustion to achieve better engine performance and lower particulate matter and oxides of nitrogen emissions. In the present study, the experiments were performed in a modified light-duty diesel engine operated in port fuel injected HCCI mode with gasoline-isobutanol blends. All the experiments were performed at a constant engine speed of 1500 rpm and varying engine loads. The effects of variations in fuel properties on the achievable load range, engine performance improvement, and emission reduction were examined. The use of isobutanol, a gasoline-like high volatile, low reactivity, renewable fuel, help reduce fossil fuel dependency. A cetane improver, 2-ethyl hexyl nitrate (2-EHN), was added in a fixed proportion of 6 vol.% to all the fuel blends to attain stable HCCI combustion at lower engine loads. The volumetric proportion of isobutanol in the fuel blends was increased from 20% to 60%, while the gasoline proportion was correspondingly reduced. An algorithm to evaluate the ‘engine performance and emission indicator value’ was used to identify suitable fuel blend composition based on user-defined weights. Test results showed that the maximum achievable engine load was extended from 38% (of rated engine load) for diesel–fuelled HCCI to 70% (of rated engine load) for isobutanol-gasoline-2-EHN-fuelled HCCI. The indicated thermal efficiency improved with increased isobutanol in the fuel blends for a particular engine load. At 50% engine load, the indicated thermal efficiency improved by 40% for 60% isobutanol/ 34% gasoline/ 6% 2-EHN than 20% isobutanol/ 74% gasoline/6% 2-EHN. The HCCI combustion of isobutanol fuel blends produced very low oxides of nitrogen and soot emissions than conventional diesel combustion, and the indicated thermal efficiency was close to that of conventional diesel combustion at lower engine loads and improved at higher engine loads. At 70% engine load, the oxides of nitrogen and soot emissions were reduced by 69% and 96%, respectively, for HCCI combustion of 60% isobutanol/34% gasoline/6% 2-EHN than conventional diesel combustion. It was found that with an increase in engine load, the optimal fuel blend composition consisted of an increased concentration of isobutanol. Overall, the present study demonstrates that isobutanol is suitable for improving HCCI engine metrics.