Homogeneous Charge Compression Ignition Combustion Research Articles

Effect of nitric oxide on the performance and emissions of a hydrogen-fueled HCCI engine

Homogeneous charge compression ignition (HCCI) engines have historically generated interest due to its potential to achieve high efficiency and low emissions. This paper presents an experimental investigation of hydrogen port fuel injection in a modified Cooperative Fuel Research (CFR) engine operated under HCCI conditions. The effect of adding nitric oxide (NO) to the intake air on engine performance, emissions, and combustion characteristics was investigated at various inlet temperatures. The experiments considered the operating regime and limitations for hydrogen HCCI engines with and without NO addition. The engine can operate over a wide range of air–fuel ratios i.e., λ = 2.7 to 4.0 at 150 OC inlet air temperature without NO addition.NO also acts as a knock promoter in reciprocating engines, limiting the engine's output. The results indicate that adding NO significantly promotes the auto-ignition of the hydrogen-air mixture, thereby extending the engine's operable range, and an ultra-lean λ of 5.0 can be reached. Our findings indicate that NO has the most notable effect on engine performance at an inlet air temperature of 90 OC. Furthermore, the results show that the addition of NO increases the amount of NOx emissions in the exhaust gas; about 50 ppm of NO was converted into NO2 during the combustion process. Adding NO to the hydrogen-air mixture has the potential to extend the engine's range of operation in HCCI providing a promising avenue for further research into HCCI combustion engines and the potential to improve efficiency.

Numerical study on the load-range extension of gasoline-fueled homogeneous charge compression ignition combustion in a light-duty diesel engine

Recent research on homogeneous charge compression ignition (HCCI) engines has demonstrated that these engines can complement traditional compression-ignition engines. The higher octane number and vapor pressure make gasoline-like fuels more suitable for port fuel-injected HCCI engines. Doping gasoline with ignition promoters eliminates intake charge preheating or turbocharging requirements and reduces cyclic variations in combustion, especially at lower engine loads. Seeding the intake charge with suitable diluents enables higher load extension of doped gasoline-fueled HCCI engines by preventing knocking. In the present study, HCCI experiments in a 0.662-litre, light-duty diesel engine using 2-Ethylhexyl nitrate (EHN)/gasoline blends formed a database for validating computational fluid dynamic (CFD) simulations. The CFD tool could capture the qualitative trends of HCCI combustion, performance, and emission parameters. The validated CFD tool was then used to investigate a suitable ignition promoter other than EHN to blend with gasoline such that a constant combustion phasing was achieved. Di-tert butyl peroxide (DTBP), hydrogen peroxide, nitric oxide, nitrogen dioxide (NO2), and ozone were the investigated ignition promoters. Further, the effects of adding diluents, including exhaust gas recirculation, nitrogen, carbon dioxide (CO2), and water vapor (H2O) on EHN-gasoline HCCI combustion, were studied for a constant combustion phasing retardation of 5 °CA towards aTDC. The primary objective of the present study was to select the most suitable ignition promoter and diluent for gasoline-fueled HCCI combustion. The results show that the least quantity of EHN and CO2 was required to control HCCI combustion phasing among the tested ignition promoters and diluents. Using NO2 as an ignition promoter and H2O vapor as a diluent improved the gross indicated thermal efficiency by 24% and 17%, respectively, compared to DTBP and EGR, which produced the lowest gross indicated thermal efficiency.

Investigation of the use of wet ethanol in an HCCI engine using water injection and direct exhaust heat recovery

Wet ethanol is a renewable fuel that has great potential to reduce the energy cost of ethanol production and improve the life-cycle carbon footprint of ethanol. The use of wet ethanol in homogeneous charge compression ignition (HCCI) mode can achieve high efficiency with low emission levels. In this context, this study investigates the effects of water-in-ethanol concentration on the performance, emissions, and combustion characteristics of an HCCI engine using water injection and recirculation of all exhaust gasses from a diesel cylinder. Water injection was used to solve the problem that there is no direct method to adjust HCCI combustion. Results showed that water–ethanol blends with higher water content had lower heat release rates and combustion temperatures, which increased the combustion duration. The indicated efficiency deteriorated for ethanol–water blends with high water concentrations. However, the highest indicated efficiency was 39.3% for the blend with 20% water by vol. at 6.0 bar. CO and organic gas emissions tended to increase with late combustion and for blends with higher water content, reaching values of 78.0 and 68.2 g/kWh at 4.0 bar, respectively. On the other hand, the NOX emissions were low, reaching a maximum value of 0.93 g/kWh in the HCCI combustion.

Effect of n-butanol additive on the combustion and emission characteristics of a coal-derived naphtha homogeneous charge compression ignition engine under different parameters

ABSTRACT The combustion and emission characteristics of n-butanol/coal-derived naphtha blends in homogeneous charge compression ignition (HCCI) combustion mode were experimentally researched on a retrofitted diesel engine. The effects of intake temperature (T in ) and excess-air coefficient (λ) were mainly analyzed. The results show that the peak in-cylinder pressure (P max ) and peak heat release rate (HRR max ) of all tested fuels show an overall increasing trend as T in rises. The combustion gets faster and more stable, carbon monoxide (CO) and hydrocarbon (HC) emissions decrease, and the indicated thermal efficiency (ITE) first increases and then decreases. When T in remains constant, the P max and HRR max decrease and the combustion phase delays as the n-butanol volume fraction increases; CO and HC emissions gradually increase, except for that of lower T in , which shows a trend of first reduction and then increase. ITE gradually decreases in general, but when T in is higher than 100°C, coal-derived naphtha containing 24% of n-butanol in volume (B24N76) exhibits the highest ITE. In addition, for all tested fuels, both P max and HRR max decrease as λ increases and the combustion gets slower and less stable; CO and HC emissions deteriorate, and ITE gradually decreases. It is worth noting that B24N76 shows the best combustion stability for all λs and exhibits the lowest CO and HC emissions when λ are 3.0 and 3.5.

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.

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.

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.

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.

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

The use of biogas fuel in homogeneous charge compression ignition (HCCI) engines has been promoted recently due to the environmental advantages. However, hydrogen sulfide (H2S) forms a non-environment friendly content and biogas impurity that its removal is associated with high costs. In this study, the effect of using biogas fuel in the HCCI engines under different operating conditions is investigated to shed light on the best scenarios of biogas combustion, even with the presence of H2S contents. A modified reaction mechanism is introduced by considering the reactions of H2S with other species in the air-fuel mixture. The new chemical kinetics model, and a multi-zone combustion approach, have been validated against experimental data from the literature and then used to simulate the HCCI combustion of biogas fuel. It was obtained that having up to 3.8% content of H2S in the intake charge can enhance the rate of heat release and combustion pressure. However, it had no significant effect on the in-cylinder temperature profile. Higher rates of H2S contents led to produce higher rates of sulfur oxides (SOx) emissions. Increasing the equivalence ratio (up to 0.50) results in a higher in-cylinder temperature and pressure as well as a higher SOx and nitrogen oxides (NOx) emissions. Also, the HCCI combustion is influenced by the intake temperature and pressure, where increasing those parameters leads to an increase in the in-cylinder temperatures and pressures, as well as the NOx emissions. However, SOx emissions are affected only when the intake temperature reaches over 400K and the intake pressure is over 1.5bar.

NUMERICAL STUDY OF WATER ADDITION ON THE COMBUSTION CHARACTERISTICS IN AN HCCI ETHANOL ENGINE

Low-temperature combustion modes have attracted global attention in recent years, especially the homogeneous charge compression ignition (HCCI) mode. The HCCI combustion produces high-speed combustion, achieving relatively high thermal efficiencies while emitting low NOX and soot. However, due to the lack of direct control to start the combustion, one of the main challenges in this type of engine is to ensure that auto-ignition occurs close to the top dead center for a wide operation range. There are a few combustion phase control techniques to solve this limitation, and one of them is water injection. In this regard, this paper explores the influence of water concentration in an ethanol HCCI engine as a form of combustion phasing control. The work was conducted numerically using a zero-dimensional single-zone model with a chemical kinetic mechanism containing 56 species and 383 reactions. The numerical model results were well agreed with the reported experimental data. The water fraction ranged from 0 to 18% by mass at 3% intervals. The results demonstrate that water injection is an efficient strategy to control the combustion phasing by adjusting the charge reactivity. The increase in water fraction reduced in-cylinder pressure and heat release rates. Furthermore, the combustion phase was advanced, the combustion duration was extended, and thermal efficiency was about 44.3% with the increase in water concentration.

Study on homogeneous charge compression ignition combustion in argon circulated closed cycle hydrogen engine

It is important to improve thermal efficiency and to reduce harmful exhaust gas emissions in internal combustion engines. A closed cycle engine system that uses a monatomic molecular gas as the working fluid can be expected to have high thermal efficiency due to the high specific heat ratio of the gas. Several studies have been reported on closed cycle engines with conventional spark ignition or compression ignition. This research newly proposes an argon circulated closed cycle homogeneous charge compression ignition (HCCI) engine system fueled with hydrogen. In this engine system, effects of in-cylinder gas initial temperature and residual water in recirculated gas on combustion characteristics were investigated. The results show that the system with argon circulation has the wider range of operable conditions and the higher thermal efficiency compared to the case with air as the working fluid.

LES of HCCI combustion of iso-octane/air in a flat-piston rapid compression machine

Homogeneous Charge Compression Ignition (HCCI) engines promise better efficiency and cleaner emissions than conventional piston engines, but can be challenging to control. Rapid compression machines (RCM) provide a simplified configuration for investigating HCCI combustion behavior, which is necessary for effective control of engine ignition timing and peak pressures. In this study, we assess the utility of large eddy simulations (LES) for predicting HCCI combustion in a 3-D configuration. To this end, LES with finite-rate chemistry employing a 99-species iso-octane/air mechanism of two RCM operating conditions are performed. The RCM configuration under consideration was designed by Strozzi et al. (Combust. Flame, 2019) with a flat piston to introduce large amounts of thermal stratification representative of realistic HCCI engine conditions, through the generation of corner vortices. It is shown that the simulation provides reasonable agreement with temperature fluctuations (7% difference), as well as ignition delay in the short ignition case (1 ms difference), while the long ignition case (35 ms difference) highlights more substantial deficiencies that are still within the expected uncertainty from the employed chemical mechanism. Flame propagation modes predicted by LES agree with experimental observations: spontaneous ignition is seen in the short ignition case, while deflagration is more prominent in the long ignition case. Analysis of global and local quantities classify the short ignition case in a mixed ignition regime, and the long ignition case in the mild ignition regime. These results demonstrate the utility of FRC-LES for investigations of multimode combustion regimes of HCCI combustion in a 3-D configuration.

Experimental investigation on operating light-duty diesel engine using ethanol–gasoline blends in a homogeneous charge compression ignition combustion mode

The advanced diesel combustion mode of homogeneous charge compression ignition (HCCI) provides simultaneous lessening of soot and oxides of nitrogen (NOx) emissions. However, HCCI operations with low volatility and high reactivity diesel fuel require energy-intensive vaporizers and suffer from a restricted operating load range. In this work, high volatility, and low reactivity ethanol–gasoline blends were utilized as fuels in a port fuel injected light-duty diesel engine operated in HCCI mode to address this limitation. To study the effect of adding ethanol to the test fuels, its content was progressively increased from 10% to 60% by simultaneously reducing the gasoline content. 6% of an ignition improver, 2-ethylhexyl nitrate (2-EHN), was added to test fuels to attain stable HCCI combustion in the test engine at lower engine loads. A combined experimental and statistical approach was followed to characterize the HCCI engine combustion, performance and emissions. The impact of independent operating factors of ethanol–gasoline fuel blend composition and engine load on the various response parameters was estimated using multi-regression models developed based on the response surface method (RSM). The optimization of engine parameters was performed using the desirability approach of RSM to maximize performance and minimize emissions. The engine operating load range was extended from 23% (1.22 bar BMEP) to 86% (4.63 bar BMEP) with ethanol–gasoline–2-EHN-fuelled HCCI, which was a substantial improvement over the achievable load range only up to 38% (2.02 bar BMEP) with diesel-fuelled HCCI. All the multi-regression models developed were statistically significant at a 95% confidence level. The results showed that the indicated thermal efficiency improved, and soot and NOx emissions reduced with increased ethanol content in the test fuels. The test engine showed optimal working conditions when operated using 49% ethanol in the test fuels at 75% engine load. To benchmark the HCCI engine performance under optimal operating conditions, it was compared with conventional diesel combustion at 75% engine load. The NOx and soot emissions decreased by 76% and 98%, respectively, while indicated thermal efficiency increased by 20% for HCCI than conventional mode. The optimal fuel reactivity was determined at various engine loads by using the model equation developed for combustion phasing. According to the findings of this study, the fuel management strategy of using ethanol and gasoline blends is a viable method to enhance the performance and emission metrics of HCCI engines.

Effects of intake charge temperature and relative air-fuel ratio on the deterministic characteristics of cyclic combustion dynamics of a HCCI engine

Homogenous charge compression ignition (HCCI) combustion can significantly reduce automotive pollution and increase the thermal efficiency of the engine. However, combustion phasing control is a major challenge in HCCI engines due to severe cyclic combustion variations. This study investigates the cyclic combustion dynamics of the HCCI engine using nonlinear dynamic methods such as return maps, recurrence plots (RPs), and recurrence quantitative analysis (RQA). Combustion stability and cyclic variations of HCCI combustion parameters were investigated on a modified four-stroke diesel engine. The experiments were conducted by varying relative air-fuel ratios ([Formula: see text]) and intake air temperatures ([Formula: see text]) at two engine speeds. In-cylinder pressure data of 2000 consecutive engine combustion cycles is logged for each test condition. In this study, deterministic characteristics of combustion phasing (CA50) and crank angle position of maximum cylinder pressure ([Formula: see text]) are investigated and compared by employing nonlinear dynamical methods. Return maps revealed that [Formula: see text] is having distinct and more frequently observed deterministic characteristics in comparison to CA50. Patterns in RPs showed a more persistent and sudden change in the combustion dynamics at higher engine speeds. Recurrence plot-based analysis found the existence of deterministic features in the combustion dynamics irrespective of the operating conditions. It was found using RQA parameters that the deterministic nature becomes stronger with a decrease in [Formula: see text] and any deviation in intermediate values of [Formula: see text]. Additionally, RQA measures advocate that CA50 has more deterministic characteristics at higher engine speed while [Formula: see text] at lower engine speed. Strong coupling and synchronization between [Formula: see text] and CA50 is indicated by cross-recurrence plots and CPR index when engine operated with a comparatively richer mixture.

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.

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.

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.

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&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.