Exhaust Gas Recirculation Ratio Research Articles

Dynamics and mitigation strategies of knock in hydrogen-fueled internal combustion engines

In the context of utilizing hydrogen as a fuel for internal combustion engines, it is crucial to address its tendency to induce knock more readily under certain conditions compared to gasoline. Knock not only reduces fuel efficiency but also has the potential to inflict detrimental effects on engine components. It is generally believed that knock is primarily caused by the spontaneous combustion of the end-gas mixture. Current research focuses on the frequency, intensity, and statistical characteristics of knock signals.This study aims to introduce two prevalent and effective methods for mitigating knock: increasing the Exhaust Gas Recirculation (EGR) ratio and water injection into the engine. Experimental observations suggest that at low rotational speeds (n=900 rpm), the amplitude spectra of knock induced by hydrogen and gasoline show similarities. However, at higher speeds (n>3000 rpm), the amplitude of hydrogen-induced knock not only exhibits a greater number of peak values but also intensifies in strength. Notably, the efficacy of increasing the EGR ratio diminishes at high speeds, potentially due to the propensity of methane to also cause knock under high-temperature conditions. In contrast, water injection, while generally effective, may adversely impact the lifespan of engine components.In summary, effective suppression of knock in hydrogen-fueled internal combustion engines is vital for accelerating the adoption of hydrogen in the power sector and making significant contributions to environmental conservation. This paper aims to delve into the analysis of these methods effectiveness and proposes directions for future research.

Effects of exhaust gas recirculation and ethanol-gasoline blends on combustion and emission characteristics of spark ignition engine

The combined influences of exhaust gas recirculation (EGR) and ethanol-gasoline blends on the combustion process and emissions of a single-cylinder spark ignition engine were numerically examined. Four different EGR values were employed, i.e. 0%, 2.5%, 5%, and 10%, to reveal the effect of EGR on engine performance. The engine was operated at a load of 100% and a speed of 3000 rpm. The peak values of in-cylinder pressure and temperature gradually decreased as increasing the EGR ratios. These peaks move towards the TDC as increasing the ethanol fraction in blends due to high oxygen in the mixture and burning flame speed in the cylinder. Ethanol fractions ranging from 5% to 15% can effectively improve the negative effects of EGR ratios. When increasing the ethanol fraction, the CO2 rapidly increased and concentrated around the TDC. The NOx emissions are significantly increased with increasing ethanol fraction. In the case of pure gasoline, the NOx emissions are substantially suppressed and exhibit a remarkably low value as increasing the EGR ratios. The best combination for diluting NOx emissions to a very low level is ethanol fraction ranging from E5 to E10, while the EGR rates range from 5% to 10%.

Performance, emissions and combustion analysis of hydrogen-enriched compressed natural gas spark ignition engine by optimized Gaussian process regression and neural network at low speed on different loads

The transportation industry is increasingly focused on hydrogen based fuel as a promising alternative due to its potential for reduced emissions and enhanced performance. The purpose of this study is to improve efficiency and reduce emissions on low speed on different loads for heavy duty vehicles. This study can be impactful to train the electronic control unit (ECU) for heavy duty vehicles working on aforementioned conditions. This study investigates the effect of hydrogen ratios (0%–40 %) in HCNG, (0%–15 %) exhaust gas recirculation (EGR) ratios, and spark timing (8°-34o CA bTDC) at low and high loads (15 % & 75 %) under stoichiometric conditions at low speed (700 rpm). Performance, emissions and combustion parameters were thoroughly analysed across these conditions. Brake thermal efficiency increases by 20.7 % & 19.4 % by the addition of (0 %–40 %) hydrogen at low and high load at 14o CA bTDC running on 5 % and 0 % EGR respectively. NOx emissions reduces by 11.9 % & 17.9 % by the addition of (0 %–15 %) EGR and increases by 46.1 % & 46.4 % by increasing the amount of hydrogen in HCNG at low and high load at 14o CA bTDC at 0 % EGR respectively. Coefficient of variation reduces 13.8 % by (0 %–40 %) hydrogen addition at 11 % EGR at 16o CA bTDC. Optimized Gaussian process regression (GPR) and neural network (NN) machine learning techniques were applied to the dataset, and found GPR matern 5/2 is best one. The findings can be utilized in the development of HCNG engine.

A Review of the Use of Hydrogen in Compression Ignition Engines with Dual-Fuel Technology and Techniques for Reducing NOx Emissions

The use of compression ignition engines (CIEs) is associated with increased greenhouse gas emissions. It is therefore necessary to research sustainable solutions and reduce the negative environmental impact of these engines. A widely studied alternative is the use of H2 in dual-fuel mode. This review has been developed to include the most recent studies on the subject to collect and compare their main conclusions on performance and emissions. Moreover, this study includes most relevant emission control strategies that have not been extensively analyzed in other reviews on the subject. The main conclusion drawn from the literature is the negative effect of the addition of H2 on NOx. This is due to the increase in temperature during combustion, which increases NOx formation, as the thermal mechanism predominates. Therefore, to reduce these emissions, three strategies have been studied, namely exhaust gas recirculation (EGR), water injection (WI), and compression ratio (CR) reduction. The effect of these techniques on NOx reduction, together with their effect on other analyzed performance parameters, have been deeply analyzed. The studies reviewed in this work indicate that hydrogen is an alternative fuel for CIEs when used in conjunction with techniques that have proven to be effective in reducing NOx.

Behavior analysis of Low-Heat Rejection engine powered by biodiesel under varied exhaust gas recirculation ratios

ABSTRACT The key focus areas of the internal combustion engine architecture are energy effectiveness and greater thermal efficiency since 1/3 of the produced heat energy vanishes on the way to the atmosphere and the coolant. Experiments have looked into the viability of using tamanu biodiesel in a thermally insulated diesel engine. The engine was first put through its paces on regular diesel fuel as a comparison baseline. After that, the piston, exhaust, intake valve and cylinder head surfaces were coated with partially stabilized zirconia (PSZ) to act as thermal insulation for the engine. The engine coating was developed to improve the efficiency of the engine’s use of biodiesel blends by decreasing heat loss through the chamber walls with a thickness of 200 micrometers (µm). In addition, mixes of Tamanu biodiesel with diesel fuel were tested, including B10, B20, B30, and B100, to examine how these mixtures would influence the performance of the ceramic-coated low heat rejection (LHR) engine compared to the performance of the base diesel engine. Additionally, the impacts of different exhaust gas recirculation (EGR) ratios on the operation of biodiesel-powered LHR engines were analyzed. The zirconia insulated LHR engine running on B20 performed the best, with a thermal efficiency of 28.57% and a brake specific energy consumption that was considerably lower than that of the baseline diesel engine. In addition, the LHR engine for B20 reduces carbon monoxide (CO) and smoke emissions by 17% and 21.4%, respectively, compared to the B20-powered base diesel engine, although nitrogen oxide (NOx) emissions slightly increase. However, the addition of 15% EGR to the B20-LHR engine produced a minor increment in hydrocarbon (HC), CO and smoke emissions, corresponding to 19.7% and 25.4%, respectively. By implementing 15% EGR with B20-LHR, the NOx level is reduced by 25.4% due to diluting the air-fuel mixture. The combination of 15% EGR with B20 for a thermal barrier-coated engine offers significant improvement by increasing engine performance and reducing emission characteristics.

Nonlinear feedforward controller design of gasoline engine air-path system for reducing engine torque overshoot

In gasoline engines, the amount of fresh air in the cylinder becomes temporarily excessive owing to the slow response in exhaust gas recirculation (EGR) gas under a high EGR ratio. This phenomenon should be avoided, as it causes an engine torque overshoot because the amount of fuel also increases to follow the stoichiometric ratio, and can cause discomfort to the driver. In this study, we investigate reducing torque overshoot using a feedforward controller, which is a simple and effective method for improving the response of a control system. The feedforward controller is typically designed based on the inverse of the plant model. However, designing a feedforward controller for a high-order and nonlinear plant, such as an engine air-path system, can be challenging. Therefore, we exploit the fact that if a given nonlinear system satisfies the flatness property, a feedforward controller based on the inverse model can be easily obtained. The effectiveness of the proposed feedforward controller is evaluated through simulations.

Study on the Effect of Coupled Internal and External EGR on Homogeneous Charge Compression Ignition under High Pressure Rise Rate

This paper investigated the effects of exhaust gas recirculation (EGR) on homogeneous charge compression ignition (HCCI) combustion in internal combustion engines. The exhaust valve closing (EVC) timings were scanned to obtain a set of baseline operating points for HCCI, and the coupling control of the internal and external EGR was explored. The results indicate that external EGR delays HCCI ignition timing and slows down the combustion speed. As the internal EGR rate increases, the maximum external EGR ratio that can be tolerated decreases. For HCCI detonation operating points with low internal EGR rates, the addition of up to 10% of external EGR can control the pressure rise rate peak to less than 10 bar/°CA, resulting in reduced fuel consumption and increased indicated mean effective pressure (IMEP). However, for HCCI operating points with high internal EGR rates, the effect of external EGR is mainly observed in the control of the pressure rise rate, with limited increase in IMEP. Additionally, an increasing external EGR rate leads to a significant decrease in nitrogen oxide (NOx) emissions, while carbon monoxide (CO) and hydrocarbon (HC) emissions slightly increase before engine misfire occurs. These findings suggest that the coupling control of internal and external EGR should be explored further, particularly in relation to reducing the negative valve overlap (NVO) angle and improving combustion efficiency.

Parametric Analysis and Optimization for Thermal Efficiency Improvement in a Turbocharged Diesel Engine with Peak Cylinder Pressure Constraints

While the original equipment manufacturers are developing engines that can withstand higher PCP, the methodology to maximize the thermal efficiency gain with different PCP limits is still not well-known or documented in the literature. This study aims to provide guidance on how to co-optimize air system parameters, compression ratio, and intake valve closing (IVC) timing of heavy-duty turbocharged diesel engines to enhance thermal efficiency with peak cylinder pressure (PCP) constraints. In this study, a one-dimensional turbocharged engine model is established and validated by experimental data. The effects of turbocharger efficiency, boost pressure, high-pressure exhaust gas recirculation (HP EGR) ratio, compression ratio (CR), and IVC timing on diesel engine efficiency are assessed under PCP constraints through parametric analysis. The results indicate that for enhancing engine thermal efficiency under limited PCP, an increment in boost pressure and CR, and late IVC timing compared to baseline is required. By multiple parameter optimization, the best parameter combination under different PCP constraints is proposed. At a PCP limit of 20 MPa, the combination of a compression ratio of 18.57, boost pressure of 298 kPa, and IVC timing of −95.2 °CA ATDC yields a 1.56% (absolute value) improvement in ITEn over the baseline condition. Raising the PCP limits from 20 MPa to 25 MPa requires increasing the compression ratio to 21.92, boost pressure to 308 kPa, and delaying the intake valve closing timing to −88.7 °CA ATDC, which results in an absolute improvement of 0.86% in ITEn. Baseline engine configuration is updated accordingly to validate the thermal efficiency improvement strategy at a 25 MPa PCP limitation. Experimental results demonstrate a 2.2% (absolute value) improvement in brake thermal efficiency and 1.98% (absolute value) improvement in overall energy efficiency.

Simulation Investigation on the Effects of EGR Ratio and Nozzle Angle on In-Cylinder Combustion and Pollutant Generation of PODE/Methanol Blends

ABSTRACT In order to explore effects of coal-based oxygenated fuels polyoxymethylene dimethyl ether (PODE) and methanol on pollutant emissions of diesel engines, in-cylinder combustion numerical model was developed by coupling PODE/methanol reaction mechanism with CONVERGE software. The influences of exhaust gas recirculation (EGR) and nozzle angle on in-cylinder combustion and pollutant generation of PODE/methanol blends were studied. Results show that with the increase of EGR ratio, the fuel-air equivalence ratio increases, the in-cylinder pressure decreases, and the ignition delay period is prolonged. The generation range and rate of NOx gradually decrease, and the final NOx generation decreases by 85.1% at EGR = 20%. However, the peak soot generation rate and the final soot generation increase. With the increase of nozzle angle, the peak in-cylinder pressure and the overall heat release rate increase. When the nozzle angle is adjusted from 148° to 164°, the rich area of fuel-air equivalent ratio in the piston pit decreases, the high temperature area in the piston pit almost disappears. The final in-cylinder NOx generation has been reduced by 29.3%. The soot distribution gradually moves to the upper layer of combustion chamber, and the peak soot generation rate decreases, while the final soot generation increases by almost 49.5%.

Review on performance and emission of spark ignition engine using exhaust gas recirculation

ABSTRACT Modernizing electronic control and developing new exhaust gas recirculation (EGR) valves have made it possible to improve EGR accuracy and shorten transient response times. With this paper, we have outlined the findings of research on the effects of various EGR ratios on engine emissions, knock suppression, and charge combustion. Results from experiments conducted by many researchers are summed up as 15% − 18% EGR is found to successfully reduce NOx emissions without impacting engine performance. Because exhaust fumes dilute the fuel/air mixture, this can lead to inefficient combustion, which can lower brake thermal efficiency. According to the findings, selecting the right EGR ratio and spark timing is essential for maximizing engine performance. examined how cold EGR affected knock intensity. It was found that the maximum compression temperature decreased in range of 30–40 kelvin and the cylinder pressure decreased up to 0.4 bar as the EGR increased from 7 to 13%. This demonstrated that the knock was effectively repressed. Because of a buildup of carbon deposits, the EGR valve frequently sticks. In addition to higher fuel consumption or poorer performance, clogged EGRs frequently result in black smoke coming from the exhaust.

A Review on Recent Developments of RCCI Engines Operated with Alternative Fuels

Environmental concerns over automotive exhaust emissions and consumer demand for higher fuel efficiency have led to the development of low-temperature combustion concepts. The reactivity-controlled compression ignition (RCCI) engine is one among them and has the potential to reduce NOx and smoke emissions simultaneously. In this concept, a low-reactivity fuel is injected into the intake port and another high-reactivity fuel is injected into the cylinder directly. This results in reactivity stratification and provides more control over the rate of heat release. However, operating parameters such as reactivity of fuels, premixing ratio, injection strategies, exhaust gas recirculation ratio, piston bowl geometry, and compression ratio influence emissions formation. The article reviews recent developments on the effect of the above operating parameters on the performance and emission characteristics of RCCI engines operated with alternative fuels. The combustion strategies used to extend the RCCI mode to higher loads are also reviewed. Applications of computational fluid dynamics (CFDs) to design the combustion chamber for RCCI engines are discussed. The need for further improvements in the CFD models for RCCI engines is explained. After presenting a thorough review of recent literature, directions for future research on RCCI engines are proposed.

Numerical simulation of the effects of the EGR ratio and ignition timing on a supercharged and high compression ratio hybrid gasoline engine

This paper explores the potential effects of the exhaust gas recirculation (EGR) ratio and ignition timing on knock suppression in a supercharged and high compression ratio (CR) hybrid gasoline engine, whereas previous knock studies have focused on conventional CRs and equivalence ratios. According to the simulation results, EGR can significantly reduce the knock intensity (KI). The high CR and EGR enable the realization of an indicated thermal efficiency of 47.46 %. Chemical modeling and solvers make free radical detection convenient. Therefore, this paper investigates the relationships between chemical kinetics and low-temperature reactions, preignition (PI) and spontaneous combustion of end mixtures (SCEM). The numerical results demonstrate that IC4H7 is an important indicator of low-temperature reactions. In the cases where SCEM and PI occur, H2O2 and CH2O substantially decompose and the masses of CH3, HCO, and CO start to decrease before the peak heat release rate (HRR) is attained. High CH2O concentration is an important indicator for high-temperature reactions, while high concentrations of CH3 and HCO can characterize the onset of SCEM or PI. The peak masses of IC4H7, HCO, and CH3 positively correlate with the KI value.

Effects of EGR on combustion and emission characteristics of PODE/methanol RCCI mode at high load

In order to extend the high-load operation range of polyoxymethylene dimethyl ethers (PODE)/methanol dual-fuel reactivity controlled compression ignition (RCCI) combustion mode, a numerical model of in-cylinder combustion was established by coupling PODE/methanol chemical reaction kinetics with CONVERGE software. And then the influence mechanism of exhaust gas recirculation (EGR) addition on in-cylinder combustion process, combustion stability and pollutant formation of the RCCI engine under high load and pilot injection strategy were investigated. The results show that with the increase of EGR ratio, the peak values of the first heat release formed by PODE pilot injection combustion and in-cylinder pressure decrease, the combustion start timing and CA50 phase are gradually delayed. While the peak value of the second heat release formed by PODE main injection combustion at low EGR ratio and the combustion duration remain unchanged. Meanwhile, as the EGR ratio increases from 0 to 30 %, the brake thermal efficiency (BTE) decreases from 46.54 % to 44.40 %. And the in-cylinder equivalent ratio and temperature field distributions become uniform, and both high-temperature region (above 1800 K) and NOx generation area are reduced, which decreases NOx emissions by 42.6 % without increasing soot emissions. The methanol mixture at squish zone is subjected to the high-temperature and high-pressure of pilot injection combustion, resulting in obvious pressure oscillation. While EGR addition decreases the generation of HCO and OH active radicals, ignition points and reaction rate, which effectively inhibits methanol spontaneous combustion and knock phenomenon, and decreases the ringing intensity from 2.82 MW/m2 to 1.50 MW/m2. The pilot injection strategy coupled with 18 % EGR can extend the indicated mean effective pressure to 1.22 MPa. However, the load further extension is mainly limited by the sharp decline of BTE.

The multi-parameter optimization of injections on double-layer diesel engines based on genetic algorithm

In this paper, a coupling model of the NSGA-II genetic algorithm and KIVA-3 V program is developed to perform a multi-objective intelligent optimization study of the injection parameters in a diesel engine with double-layer diverging combustion (DLDC) chamber. Four optimization parameters, involving the first injection timing, the first fuel split ratio, the injection timing interval, and the exhaust gas recirculation (EGR) ratio, are optimized after comparing the pollutant emissions and fuel consumption characteristics. The computation results reveal that both soot and fuel consumption function as the optimization objectives, proving a trade-off relationship with the NOx emission. The analysis of the response surface demonstrates that the application of the multiple-injection strategies is beneficial for enhancing the performance of diesel engines. A large first fuel split ratio and a low EGR rate can minimize both ISFC (indicated specific fuel consumption) and soot emission concurrently. A high EGR rate can significantly reduce NOx emission. In addition, the distribution of the final Pareto font shows that 66.7 % percent of the first fuel split ratio is above 0.56, and only two solutions (8.3 %) have values below 0.35. Furthermore, three representative points of the first fuel split ratio are selected for combustion analysis, which are 0.05, 0.35, and 0.88. As the first fuel split ratio rises, the high-temperature areas in the cylinder are gradually enlarged, and the NOx emission is increased while the soot emission and ISFC are further reduced.

Sustainable biodiesel from flex-mix feedstock and its combustion in a VCR-CRDI engine with variable exhaust gas recirculation and injection pressure

Biodiesel produced from single feedstocks has many challenges due to variations in the oil properties. The flex-mix approach is a long-term solution for turning mixed feedstock into high-quality biodiesels. In this investigation, a pre-mixed used cooking oil and animal fat (pig fat) mixture (from 20% to 80%) was transesterified to produce flex-mix methyl ester (FMME). The FMME fuel characteristics were tested and compared to biodiesel standards. Generally, biodiesel emits higher oxides of nitrogen (NO x ) gas due to the presence of highly unsaturated compounds and oxygen. The present study aims to address this issue by adopting the flex-mix approach in combination with fuel injection strategies (400, 500 and 600 bar), exhaust gas recirculation (EGR 10%, 20% and 30%) and variable compression ratio (CR 17.5:1, 20:1 and 22:1). At a CR of 22 and an injection pressure (P inj) of 600 bar, the FMME fuel without EGR shows a minimum reduction in brake thermal efficiency of 0.15% when compared to diesel. Nitric oxide gas emissions decreased by nearly 50% for all P inj and EGR values, but they rose when the compression ratio was increased to 20 and 22. Smoke and hydrocarbon emissions also increased with the exhaust gas proportion. The engine performance with FMME fuel was found to be equivalent to that with fossil diesel fuel. According to the findings, the flex-mix approach could be a long-term alternative to producing renewable fuel for off-road diesel engine application.

Effect of Exhaust Gas Recirculation and Spark Timing on Combustion and Emission Performance of an Oxygen-Enriched Gasoline Engine.

Oxygen-enriched combustion (OEC) technology in SI engines can greatly improve the degree of constant volume combustion, increase the torque output, and reduce HC and CO emissions but lead to a sharp increase in NO x emissions. Simultaneously, the high temperature from OEC would lead to high nucleation particle emissions. Under the OEC mode, except the oxygen content, spark timing and engine load are important influencing factors on emissions. Exhaust gas recirculation (EGR) technology has been proven to reduce NO x emissions effectively. This research investigates the effects of EGR on combustion and emission performance under an oxygen-enriched ratio (OER) of 25% with five EGR ratios (0-20%) for the initial throttle opening of 14% (at an EGR ratio of 0%) with an engine speed of 1500 rpm. The study shows that when the OER is 25%, the output torque increases with the increase of the EGR ratio. At the proper spark timing, the EGR ratio over 15% can obtain lower NO x emissions and particle emissions than the baseline (OER of 21%). Although HC emissions increase with the EGR ratio, they are still lower than the baseline. Overall, the OER of 25% coupled with the EGR ratios of 15-20% is the predominant combustion mode to improve power and emission performance in SI engines.

Simulation study on effects of EGR ratio and compression ratio on combustion and emission characteristics of PODE/methanol RCCI engine

In order to solve the problems of combustion instability and emission deterioration of reactivity controlled compression ignition (RCCI) engine under high load, the in-cylinder combustion model of polyoxymethylene dimethyl ethers (PODE)/methanol dual-fuel RCCI engine was constructed by CONVERGE software coupling with chemical reaction mechanism, and the influence mechanism of exhaust gas recirculation (EGR) ratio and compression ratio (CR) on engine performance, in-cylinder combustion and emission characteristics of PODE/methanol RCCI mode was systematically studied. Results show that with the increase of EGR ratio, the combustion phase of RCCI mode is gradually delayed, the ignition delay and combustion duration are extended, the CA50 phase is gradually delayed, the combustion temperature decreases, the mixture distribution becomes more uniform, and the combustion process becomes smoother. When the EGR ratio increases from 0 % to 30 %, NOx production is reduced by 47.3 %, ringing intensity (RI) and maximum pressure rise rate (MPRR) decreases by 1.31 MW/m2 and 0.37 MPa/°CA respectively, and brake thermal efficiency (BTE) decreases from 45.45 % to 43.19 %. With the reduction of CR, the combustion start point is gradually postponed, the peak heat release rate and combustion temperature continuously decrease, and both IMEP and BTE show a downward trend. The variation of CR breaks the trade-off relationship between NOx and soot, and improves combustion stability, but it is also limited by the BTE reduction. When the CR decreases from 17.5 to 15.5, NOx and soot production are reduced by 28.58 % and 20.1 %, RI and MPRR are reduced by 1.26 MW/m2 and 0.7 MPa/°CA respectively, and BTE decreases from 45.45 % to 44.52 %. Therefore, the CR of 16.5 is more suitable for stable operation of PODE/methanol dual-fuel RCCI engine at high load.

Emissions Characteristics and Engine Performance from the Interaction Effect of EGR and Diesel-Ethanol Blends in Diesel Engine

Recently, most of the researchers focused on provide lower greenhouse gas emissions that emitted from diesel engines by using renewable fuels to be good alternative to the conventional diesel fuel. Ethanol can be derived from renewable sources such as sugar cane, corn, timber and dates. In the current study, the ethanol fuel used in the tests was derived from the dates. The effects of using exhaust gas recirculation (EGR) diesel-ethanol blend (E10) with on engine performance and emissions characteristics have been studied in diesel engine under various engine loads. This study focused the use of oxygen in the bio-ethanol composition to compensate for the decrease occurred by the addition of EGR, which improves the engine performance and reduces its emissions. In this experiment, the ratios of EGR were 10%, 20% and 30% as well as 10% ratio of ethanol was blended into the diesel fuel blend under fixed engine speed. A traditional (without additional systems to reduce emissions) four cylinders direct injection (DI) diesel engine was used for all tests. The brake specific fuel consumption (BSFC) increased with increasing the EGR ratio by 10%, 20% and 30% by 18.7%, 22.4% and 37.4%, respectively. The thermal efficiency decreased under variable conditions of engine load for different ethanol blends. Furthermore, the emissions of NOX decreased when fuelled B10 into the engine in comparison with diesel under low engine load. Significant reduction in the NOx emissions were found when applied EGR in the tests than to the absence EGR for E10 blend and diesel. The NOx reduction rate was 12.3%, 30.6% and 43.4% when EGR rate was 10%, 20% and 30%, respectively. In addition, the concentrations of HC and CO emissions decreased more by 8.23% and 6.4%, respectively, when using E10 in comparison with the diesel for various engine loads. It is indicated that the oxygen reduction by EGR effect was compensated from ethanol blend combustion. The results showed that the combination use of E10 and EGR leads to significant reduction in engine emissions accompanied with partial reduction in the engine performance.

Combustion and emission characteristics of diesel engine fueled with diesel/cyclohexanol blend fuels under different exhaust gas recirculation ratios and injection timings

Cyclohexanol is obtained from abundant lignocellulosic biomass sources at low cost, and it is a promising alternative fuel for diesel engines. In this study, cyclohexanol was blended with diesel at various volume ratios and the mixtures were denoted as D100 (100 % diesel + 0 % cyclohexanol), D90CH10 (90 % diesel + 10 % cyclohexanol), and D80CH20 (80 % diesel + 20 % cyclohexanol), respectively. Subsequently, the effects of exhaust gas recirculation and pilot plus main injections at various pilot injection timings on the combustion and emissions of the diesel engine fueled with various mixtures were evaluated. The results demonstrated that diesel/cyclohexanol blends had a longer ignition delay, but shorter combustion duration. D80CH20 had the highest oxygen content, peak combustion temperature (PCT), and peak heat release rate (PHRR) at medium and high loads. Cyclohexanol blending with diesel significantly decreased the particulate number (PN) and volume concentrations at the expense of higher NOx emissions. Advancing the pilot injection timing prolonged the ignition delay and combustion duration, and increased the PCT and PHRR. Therefore, it emitted higher NOx emissions, but lower PN emissions. D80CH20 with 8 % EGR can simultaneously reduce the PN and NOx emissions at medium and high loads.

EFFECT OF EGR ON COMBUSTION AND EMISSION CHARACTERISTICS IN DIESEL BIOETHANOL DUAL-FUEL ENGINE

The diminution of global fossil fuel reserves is a main concern and alternative fuel sources are needed to tackle the issue of global warming caused by greenhouse gases. Biofuels have been considered as an alternative to the depleting oil resources. This study investigates the effect of exhaust gas recirculation (EGR) on combustion, performance and emission characteristics in a single-cylinder reactivity-controlled compression ignition engine using diesel-bioethanol as fuel. A dual-fueling strategy is achieved such that bioethanol is introduced into the intake manifold using a port-fuel injector (PFI) while diesel is directly injected into the combustion chamber. Various percentage of EGR rate were considered and compared. The important parameters that were taken into consideration are: engine efficiency, combustion characteristics, and exhaust gas emissions. Experimental results revealed that the EGR variation had a noticeable effect on the engine performance, emissions, and combustion characteristics with diesel-bioethanol dual fuel operation. Introduction of EGR has effectively reduced the combustion pressure rise rate along with keeping the NOx emission within the legislation norm. Besides, the results also revealed that the diesel-bioethanol dual fuel combustion has low smoke emission across all EGR ratios. Lastly, the results showed that the engine operating under diesel-bioethanol fueling could achieve high efficiency with near zero nitrogen oxides (NOx) and smoke emissions.