Exhaust Gas Recirculation Ratio Research Articles

Effect of addition of hydrogen and TiO2 in gasoline engine in various exhaust gas recirculation ratio

The effects of hydrogen ratios on combustion and emission characteristics of gasoline engine were studied under different exhaust gas recirculation (EGR), ignition timing and ignition pressure. The test performed in a modified gasoline direct ignition engine at different hydrogen ratios of 0%, 5%, 10% and 25%. In addition, the EGR rate set to 0%, 5%, 10% and 20% to study the combustion and emission characteristics. Addition to the different hydrogen fractions, 5% of TiO2 is added to increase the combustion characteristics with reduced emission. Regarding the results of the current study, the engine torque increases by 15% due to the addition of hydrogen in gasoline, while mechanical efficiency is improved by achieving a large throttle opening. At the same time, NOx emission decreased by 62% compared to the unmodified engine due to the influence of EGR, hydrogen ratio and high oxygen concentration TiO2. Moreover, the emission of CO and HC also reduced due to the influence of hydrogen fuel. Additionally, few more tests are taken to monitor the effect of the injection pressure for the hydrogen fuel. Higher injection reports higher effective thermal efficiency at 4 MPa and lower NOx. Reasonable injection pressure results in shorten flame development period.

The impact of water injection and exhaust gas recirculation on combustion and emissions in a heavy-duty compression ignition engine operated on diesel and gasoline

Steady-state experiments were conducted on a 12.4L, six-cylinder heavy-duty engine to investigate the influence of port-injected water and dilution via exhaust gas recirculation (EGR) on combustion and emissions for diesel and gasoline operation. Adding a diluent to the combustion process reduces peak combustion temperatures and can reduce the reactivity of the charge, thereby increasing the ignition-delay and, allowing for more time to premix air and fuel. Experiments spanned water/fuel mass ratios up to 140mass% and exhaust gas recirculation ratios up to 20vol% for gasoline and diesel operation with different injection strategies. Diluting the combustion process with either water or EGR resulted in a significant reduction in nitrogen oxide emissions along with a reduction in brake thermal efficiency. The sensitivity of brake thermal efficiency to water and EGR varied among the fuels and injection strategies investigated. An efficiency breakdown revealed that water injection considerably reduced the wall heat transfer; however, a substantial increase in exhaust enthalpy offset the reduction in wall heat transfer and led to a reduction in brake thermal efficiency. Regular diesel operation with main and post injection exhibited a brake thermal efficiency of 45.8% and a 0.3% reduction at a water/fuel ratio of 120%. The engine operation with gasoline, early pilot, and main injection strategy showed a brake thermal efficiency of 45.0% at 0% water/fuel ratio, and a 1.2% decrease in brake thermal efficiency for a water/fuel ratio of 140%. Using EGR as a diluent reduced the brake thermal efficiency by 0.3% for diesel operation, comparing ratios of 0% and 20% EGR. However, a higher impact on brake thermal efficiency was seen for gasoline operation with early pilot and main injection strategy, with a reduction of about 0.8% comparing 0% and 20% EGR. Dilution by means of EGR exhibited a reduction in nitrogen oxide emissions up to 15 g/kWh; water injection showed only up to 10 g/kWh reduction for the EGR rates and water/fuel ratio investigated.

Effect of Exhaust Gas Recirculation Rate on the Emissions of Persistent Organic Pollutants from a Diesel Engine

This study investigates the emission characteristics of toxic organic pollutants (PAHs, PCDD/Fs, and PCBs) generated by a heavy-duty diesel engine operating at various exhaust gas recirculation (EGR) rates during steady-state cycles. Tests on the exhaust gas composition were conducted before and after changing the EGR ratio. The fuel used in the study (B2 diesel) was a mixture of 2% biodiesel and 98% diesel. The main focus was on the emission factors for the organic toxic pollutants in the exhaust gas after EGR ratios of 0% and 5% were applied. At an EGR ratio of 5%, the total mass emission factors for the PAHs and PCBs increased by 9.1 times and 14.4 times, respectively, while the toxicity equivalent factors increased by 4.0 times and 4.8 times, respectively. A significant increase in pollutants with a higher molecular weight, particularly for the PAHs, was observed after applying an EGR ratio of 5%, implying incomplete combustion. The emission factors of carbon dioxide (CO2) and nitric oxides (NOx) decreased by 2.5% and 54.4%, respectively, when the EGR ratio was increased from 0% to 5%, but those of PM and carbon monoxide (CO) increased by 60.5% and 66%, respectively. Therefore, a combination of control strategies is necessary in order to achieve a significant reduction in the emission of all pollutants.

Insights into engine autoignition: Combining engine thermodynamic trajectory and fuel ignition delay iso-contour

One of the ultimate goals of chemical kinetic study is to understand and predict autoignition in engines. In this study, utilizing toluene primary reference fuels (TPRF) as a gasoline surrogate and a recently developed multicomponent gasoline kinetic mechanism, we have demonstrated a general approach to analyze autoignition in arbitrary spark-ignition (SI) and advanced compression ignition (ACI) engine conditions by combining thermodynamic pressure-temperature trajectory and the fuel ignition delay iso-contours. This method allows direct evaluation of controlling chemistry, potential involvement of low temperature heat release, and the dependence of autoignition to conventional fuel metrics (research and motor octane rating, i.e., RON and MON, and octane sensitivity OS = RON-MON) and engine operating conditions such as equivalence ratio, exhaust gas recirculation (EGR) ratio and engine intake conditions. Applying the analysis to the pressure-temperature trajectories of the conventional RON and MON tests, as well as those beyond RON and beyond MON, distinct roles of conventional gasoline fuel metrics and engine operating parameters are identified for all representative engine conditions. By comparing the autoignition behavior in ACI and SI engine conditions, the knowledge obtained from SI engine knock cannot be directly transferred to ACI bulk combustion phasing control in general, due to the different mixture equivalence ratios and the associated differences in reactivity and its dependence. This method could be extended to generate an auto-ignition map for arbitrary fuels and arbitrary engine trajectories, and the useful insights and overall evaluations can be used to complement conventional kinetic simulation of engine cycles.

A novel fuzzy logic variable geometry turbocharger and exhaust gas recirculation control scheme for optimizing the performance and emissions of a diesel engine

Variable geometry turbocharger and exhaust gas recirculation valves are widely installed on diesel engines to allow optimized control of intake air mass flow and exhaust gas recirculation ratio. The positions of variable geometry turbocharger vanes and exhaust gas recirculation valve are predominantly regulated by dual-loop proportional–integral–derivative controllers to achieve predefined set-points of intake air pressure and exhaust gas recirculation mass flow. The set-points are determined by extensive mapping of the intake air pressure and exhaust gas recirculation mass flow against various engine speeds and loads concerning engine performance and emissions. However, due to the inherent nonlinearities of diesel engines and the strong interferences between variable geometry turbocharger and exhaust gas recirculation, an extensive map of gains for the P, I, and D terms of the proportional–integral–derivative controllers is required to achieve desired control performance. The present simulation study proposes a novel fuzzy logic control scheme to determine appropriate positions of variable geometry turbocharger vanes and exhaust gas recirculation valve in real-time. Once determined, the actual positions of the vanes and valve are regulated by two local proportional–integral–derivative controllers. The fuzzy logic control rules are derived based on an understanding of the interactions among the variable geometry turbocharger, exhaust gas recirculation, and diesel engine. The results obtained from an experimentally validated one-dimensional transient diesel engine model showed that the proposed fuzzy logic control scheme is capable of efficiently optimizing variable geometry turbocharger and exhaust gas recirculation positions under transient engine operating conditions in real-time. Compared to the baseline proportional–integral–derivative controllers approach, both engine’s efficiency and total turbo efficiency have been improved by the proposed fuzzy logic control scheme while NOx and soot emissions have been significantly reduced by 34% and 82%, respectively.

Impact of exhaust gas recirculation on ignition delay times of gasoline fuel: An experimental and modeling study

The ignition delay times of a research grade gasoline, RON95E10, are measured in a rapid compression machine and in a shock tube. The experiments are carried out for fuel/O2/Ar/N2 mixtures with two equivalence ratios of 0.77 and 1.18 at pressures between 20 and 40 bar over the temperature range of 700–1250 K. In particular, data are reported for two exhaust gas recirculation (EGR) loadings of 0 and 25% to demonstrate the impact of EGR on gasoline ignition delay times. The presented data are, to the authors’ knowledge, the first set of ignition delay times of real gasoline with EGR and at engine relevant high pressures covering the entire intermediate temperature range. A published gasoline mechanism (Cai and Pitsch, 2015) is modified as part of this study following the latest kinetic knowledge and is further used to compute the ignition delay times at the conditions experimentally investigated. The simulations employ a four-component surrogate consisting of n-heptane, iso-octane, toluene, and ethanol. It is shown that the proposed model predicts the total ignition delay times of gasoline accurately under various conditions and reflects correctly the influences of pressure, EGR, and equivalence ratio on ignition delay times, while it fails to predict the first stage ignition delay times with very high accuracy due to the neglect of the olefin and naphthene content in the surrogate formulation. Furthermore, the influence of exhaust gas addition on ignition delay times is analyzed and discussed in more detail using results from numerical simulations. The chemical impact of EGR is minor but not negligible and varies at different conditions depending on the EGR composition.

Effects of Exhaust Gas Recirculation on Knock Intensity of a Downsized Gasoline Spark Ignition Engine

Exhaust gas recirculation (EGR) has gained prominence as a significant method to control port fuel injection engine knock caused by high compression ratio and high intake pressure (IP). In this paper, the effect of EGR on knock intensity was investigated under various conditions which included different compression ratios (9:1, 10:1, 11:1), IPs (1.0 bar, 1.2 bar, 1.4 bar) and intake temperatures (ITs, 20 °C, 40 °C, 60 °C). The torque output being a crucial variant was also considered. The results showed that EGR effectively reduced the maximum amplitude of pressure oscillations (MAPO) and knock intensity factor (KI20). The effect of EGR on knock resistance was more significant at higher compression ratio, IP, and IT. The output torque of the engine reached a peak value with a suitable EGR ratio which also controlled the intensity of knock under different conditions.

Investigation of the thermal effects of fuel injection into retained residuals in HCCI engine

Low-temperature combustion in reciprocating engines appears to be a cutting-edge technology which ensures extremely low emissions of nitrogen oxides and particulate matters in parallel with high fuel efficiency. This mode of combustion can be realized in homogeneous charge compression ignition engines. However, this technology poses challenges, and fast response combustion controllability is one of the issues to be solved to make this concept widely applicable. The introduction of direct injection of gasoline into recompressed residuals during negative valve overlap is one of the promising techniques to keep the advantages of having a homogeneous mixture during the main combustion while adding controllability through split ratio and injection timing within the recompression event.The present study aims to thoroughly investigate the thermal effects associated with gasoline injection during the negative valve overlap phase and explain qualitatively and quantitatively their impact on the gas exchange process and, further, on the combustion phasing during the main event. Single cylinder engine experiments are designed to evaluate these effects at different injection timings and mixture compositions. The scope of the research is focused on low-load operation at constant engine speed. The discussion of in-cylinder pressure analysis results and engine operational parameters is complemented by gas exchange simulations to provide more insight into the entire working process.It is confirmed by the results that negative valve overlap gasoline injection can be used as a measure to control combustion phasing in homogeneous charge compression ignition engines. The controllability is assured through balancing between evaporative cooling or heating of the trapped residuals. With this measure effective regulation of internal exhaust gas recirculation ratio, ranging from 41% to 64%, was demonstrated. This further enables fast intake valve closing temperature adjustment in a range of around 50 K, which finally results in superior auto-ignition timing control in a range between 5 °CA and 10 °CA before or after top dead center, depending on the global mixture strength. The work further provides fundamental understanding of the regulation mechanisms and concludes on the possibilities of applying this knowledge in a production engine.

A study on combustion characteristics under enriched-oxygen condition by exergy analysis

The object of this paper is to investigate the effect of operating parameters on Oxygen-enriched combustion (OEC) by exergy balance analysis during methane combustion process. In this work, the specific exergy value of fuel, feed gas and products were calculated on the basis of the second law of thermodynamics in different reaction conditions, so that availability destructions and exergy efficiencies of OEC process can be obtained based on exergy balance, and the influence of initial fuel temperature, oxygen concentration, exhaust gas recirculation ratio and equivalence ratio were addressed. It is observed that during methane OEC process, the exergy efficiency is mainly affected by products temperature, in the case of products temperature lower than 1870K, exergy efficiency of combustion increase with products temperature, and opposite changes was appeared when the products temperature higher than 1870K. Meanwhile, appropriate control of equivalence ratio can also be used to improve exergy efficiency by suppressing the dissociation of product.

Effect of Heavy-Duty Diesel Engine Operating Parameters on Particle Number and Size Distribution at Low Speed Condition

Experiments and simulations were used to investigate the effect of a range of engine operating parameters and fuel characteristics on the particle size and particle number (PN) concentration at low speed and idle speed condition. The occurrence, size, and concentration of particles were tested against a range of parameters including start of injection (SOI), common rail pressure, exhaust gas recirculation (EGR) ratio and load. The results showed that the homogeneity of the mixture had the greatest impact on particle size and number concentration. The performance of particle is different at different levels of load. The particle were of nucleation mode at idle condition, and the cold idle particles had a slightly larger diameter than those produced at hot idle. By using the diesel and under high load, at EGR ratios of less than 20 %, most particles were of nucleation mode. At EGR ratios exceeding 20 %, nucleation-mode particles were gradually replaced by accumulation-mode particles. At EGR ratios above 30 %, most particles were of the accumulation mode. Under the same load, gasoline compression ignition produced particles of smaller size and reduced particulate mass (PM). The use of gasoline extended ignition delay, as the high volatility and octane number of the fuel improved the homogeneity of the mixture. Finally, a linear relationship was found between PM and PN. The relative contribution of the different factors to the formation of nucleationor accumulation-mode particles was investigated.

Laminar flame properties of C1-C3 alkanes/hydrogen blends at gas engine conditions

The use of fuel blending is encouraged in order to achieve more flexibility in gas engines. In order to design such engines effectively, relevant information about the laminar flame speeds and laminar flame thickness are necessary. Hydrodynamic and thermo-diffusive instabilities at gas engine conditions prevent the acquisition of reliable data experimentally. One-dimensional numerical simulations with detailed chemistry can be a solution. A huge database of laminar flame speeds is generated covering a broad range of gas engine applications, pressure (p) 0.1–20 MPa, fresh gas temperature (Tu) 300–1100 K, air-fuel equivalence ratio (λ) 0.9–2.5, methane 100–60 vol%, ethane 0–40 vol%, propane 0–40 vol%, hydrogen 0–30 vol% and exhaust gas recirculation (EGR) 0–30 m%. The detailed reaction mechanisms GRI 3.0 and AramcoMech 1.3 are used for the generation of flame speed data for the mentioned conditions. A laminar flame speed correlation for 100% hydrogen extending up to elevated pressure and temperature conditions is developed. A blending law based on Le Chatelier’s rule is investigated. It is observed that the HC-ratio has a very determining effect for the laminar flame properties of different C1-C3 alkane blends. Based on this observation, it was possible to derive a very efficient correlation for both laminar flame speed and laminar flame thickness for the group of natural gas blends with methane, ethane, propane and hydrogen, and as well as including relevant EGR, which corresponds within 7% accuracy to the calculated database of about 73,000 points. The developed laminar flame speed correlation is incorporated in an engine process simulation code. It is validated with the measured in-cylinder pressure traces from the single cylinder research engine experiments for different gas blends and EGR ratios.

Self-Humidification of a Polymer Electrolyte Membrane Fuel Cell System With Cathodic Exhaust Gas Recirculation

Water management is critical for the operation of a polymer electrolyte membrane fuel cell (PEMFC). For the purposes of high power and long working-lifetime of PEMFCs, external humidifiers are always utilized as a necessary part of balance of plants to keep the imported air and fuel wet. However, they have several disadvantages, and it is beneficial to remove them so as to reduce system volume and to enhance the cold-starting capability. In this paper, a self-humidified PEMFC of an active area 250 cm2 and cell number 320 is proposed and investigated. The imported dry air on the cathode side is mixed with moisty exhaust gas by using a recirculation valve, and the dry hydrogen on the anode side is humidified by back-diffusion water through the membrane. A nonlinear model is set up based on mass transport and energy conservation equations to capture dynamics of gases in the supply and exhaust manifolds, the gas diffusion layers (GDLs), and the membrane. An analysis is conducted to investigate the influences of parameters on dynamic and stable performances. Simulation results show that system performances can be greatly affected by parameters such as air stoichiometry, current density, exhaust gas recirculation (EGR) ratio, and membrane thickness. By accurately controlling the EGR ratio and carefully selecting design and operation parameters, it is probably for a PEMFC without an external humidifier to have similar system efficiency compared to a traditional system.

A Detailed Study of the Effects of Biodiesel Addition and Exhaust Gas Recirculation on Diesel Engine PCCI Combustion, Performance and Emission Characteristics by KIVA–CHEMKIN Coupling

In this study, a numerical study is performed by KIVA–CHEMKIN code to investigate the effects of biodiesel addition and exhaust gas recirculation (EGR) on diesel engine premixed charge compression ignition (PCCI) combustion, performance, and emission characteristics. The studies are performed for neat diesel fuel and mixture of 10–40% biodiesel addition at 67%, 50%, and 40% EGR. For this purpose, a multichemistry surrogate mechanism using methyl decanoate (MD) and methyl-9-decenoate (MD9D) is used. The main innovation of this work is analyzing the chemical, thermodynamic, and dilution effects of biodiesel addition as well as different EGR ratios on PCCI combustion behavior. The results show that the main effect of EGR on PCCI combustion of biodiesel blend is related to the high temperature heat release (HTHR), and its effect on low temperature heat release (LTHR) is low. With increasing biodiesel addition, the role of the chemical effect is increased compared to the thermodynamic and dilution effects. Rate of production analysis (ROPA) indicate that for the different biodiesel ratios, the effect of reaction nC7H16 + HO2 = C7H15-2 + H2O2 is more effective on the start of combustion (SOC) compared to the other reactions. For a defined biodiesel addition, with decreasing EGR, total (unburned) hydrocarbon (THC) and CO are decreased, while NOx and indicated specific fuel consumption (ISFC) are increased.

Model-based control of diesel engines with multiple fuel injections

We developed a feed-forward controller for a conventional diesel combustion engine with triple fuel injection and experimentally evaluated its performance. A combustion model that discretizes an engine cycle into a number of representative points to achieve a light calculation load is embedded into the controller; this model predicts the in-cylinder gas-pressure-peak timing with information about the operating condition obtained from the engine control unit. The controller calculates the optimal main-fuel-injection timing to control the in-cylinder gas-pressure peak using the prediction result as a controller with a single input and output. The controller’s performance was evaluated by experiments using a four-cylinder diesel engine under changing the target value of the in-cylinder gas-pressure-peak timing during a target-following test and the performance was also evaluated under changing the exhaust gas recirculation ratio at the constant target value of the in-cylinder gas-pressure-peak timing for the disturbance-response test. It was found that the controller could calculate the optimal main-injection timing over a cycle and maintain the targeted in-cylinder gas-pressure-peak timing even when the target value or exhaust gas recirculation changed. The combustion model was also shown to be fast enough at predicting diesel combustion for onboard control.

Emission Characteristics for a Homogeneous Charged Compression Ignition Diesel Engine with Exhaust Gas Recirculation Using Split Injection Methodology

Due to the serious issues caused by air pollution and global warming, emission regulations are becoming stricter. New technologies that reduce NOx and PM emissions are needed. To cope with these social exhaust gas regulation demands, many advanced countries are striving to develop eco-friendly vehicles in order to respond to stricter emissions regulations. The homogeneous charged compression ignition engine (HCCI) incorporates a multi-stage combustion engine with multiple combustion modes, catalyst, direct fuel injection and partial mixing combustion. In this study, the HCCI combustion was applied to analyze and review the results of engines applying HCCI combustion without altering the conventional engine specifications. The optimization of exhaust gas recirculation (EGR) and compression ratio changes provides an optimal fuel economy. In this study, potential for optimum economy within the range of IMEP 0.8 MPa has been evaluated.

Performance and emission characteristics of CIE using hydrogen, biodiesel, and massive EGR

Hydrogen is considered as an excellent energy carrier and can be used in diesel engines that operate in dual fuel mode. Many studies have shown that biodiesel, which is sustainable, clean, and safe, a good alternative to fossil fuel. However, tests have confirmed that using biodiesel or hydrogen as a fuel or added fuel in compression ignition engines increases NOx concentrations. Cooled or hot exhaust gas recirculation (EGR) effectively controls the NOx outflows of diesel engines. However, this technique is restricted by high particulate matter PM emissions and the low thermal efficiency of diesel engines.In this study, gaseous hydrogen was added to the intake manifold of a diesel engine that uses biodiesel fuel as pilot fuel. The investigation was conducted under heavy-EGR conditions. An EGR system was modified to achieve the highest possible control on the EGR ratio and temperature. Hot EGR was recirculated directly from the engine exhaust to the intake manifold. A heat exchanger was utilized to maintain the temperature of the cooled EGR at 25 °C.The supplied hydrogen increased NOx concentrations in the exhaust gas emissions and high EGR rates reduced the brake thermal efficiency. The reduction in NOx emissions depended on the added hydrogen and the EGR ratios when compared with pure diesel combustion. Adding hydrogen to significant amounts of recycled exhaust gas reduced the CO, PM, and unburned hydrocarbon (HC) emissions significantly. Results showed that using hydrogen and biodiesel increases engine noise, which is reduced by adding high levels of EGR.

Development and validation of a new reduced diesel-n-butanol blends mechanism for engine applications

A reduced n-heptane-toluene-n-butanol-polycyclic aromatic hydrocarbon (PAH) combustion mechanism was developed for a blended fuel of n-butanol and diesel, including 101 species and 531 reactions. A sensitivity analysis was conducted for the optimization of the mechanism. The optimized mechanism was widely validated with ignition delays, laminar flame speeds, species concentrations in premixed flame and counterflow flame, and homogeneous charge compression ignition (HCCI) engine combustion. According to the validation results, the optimized mechanism shows favorable predictions, especially on the important species related to the PAH formation. Moreover, the reduced mechanism was coupled with computational fluid dynamic (CFD) to conduct direct injection compression ignition (DICI) engine tests within a wide range of exhaust gas recirculation (EGR) ratio and also shows favorable prediction results. Therefore, the proposed mechanism can be used to simulate the combustion of diesel or n-butanol-diesel blends in multi-dimensional CFD modeling. Besides, the main formation pathways of benzene (A1), a precursor of soot, were analyzed in a single-zone HCCI engine model. Results show that, in addition to the traditional pathways of ‘C4+C2’ and ‘C3+C3’, toluene was quite crucial to produce A1. The counterflow flame validation tests also demonstrated the importance of the addition of toluene to the PAH and soot formation. In the early combustion period, C6H5OH significantly contributed to the formation of A1, while toluene directly produced a large amount of C6H5CH2 and thus promoted the formation of A1. In the middle combustion period, OC6H4CH3 played an important role in the formation of A1, while toluene made less contribution.

A phenomenological model of knock intensity in spark-ignition engines

In experimental calibration of mass production spark-ignition (SI) engines, knocking cycles are usually determined by a specified threshold of knock intensity (KI). In engine cycle simulation, however, modeling of knock is usually limited to prediction of knock onset (i.e. auto-ignition of end gas), or merely simple parameters such as unburned mass fraction (UMF) for KI are taken into account, causing considerable deviation from actuality. The objective of this study is to develop a phenomenological KI model to improve predictability of engine cycle simulation. The experiments with a turbocharged 1.5L gasoline engine operated by spark sweeps around knock limits over a wide speed range are conducted to generate the data base for the model formulation and evaluation. With assumption of lognormal distribution of KI in consecutive cycles, a knock factor (KF) based on the likelihood ratio is proposed as a criterion for definition of knocking cycles. The model developed in the previous study, which includes the cylinder pressure, end gas temperature, exhaust gas recirculation (EGR) ratio and excess air ratio as variables, is used to predict the knock onset. With in-depth analysis of the physics influencing knock intensity, the energy density and heat release rate (HRR) in hot spots are identified to play critical roles in determination of knock intensity. The heat release rate is related to the end gas temperature, pressure, EGR ratio and excess air ratio, while the energy density is determined by the amount of fresh charge in the cylinder and the charge volume at knock onset. Thus, the correlation of the two factors, including the HRR factor α and the energy density factor β, is formulated to develop the predictive model of knock intensity YKI. Finally, the newly developed KI model is evaluated through comparison with other KI models, and better performance in terms of prediction of knock intensity is obtained.

Numerical study of exhaust reforming characteristics on hydrogen production for a marine engine fueled with LNG

When the engine exhaust heat is used for catalytically reforming the mixtures of natural gas and partial exhaust to produce the on-board hydrogen, the hydrogen-rich combustion can be achieved to improve the combustion performance of the natural gas engine. In this work, according to the Exhaust Gas Recirculation (EGR) system of a LNG-fueled engine, an exhaust reforming reaction tube of the reformer with interior coated Ni-based catalyst was modeled with full computational fluid dynamics (CFD) combined with detailed chemical reaction mechanisms to study the reforming characteristics when the EGR ratio ranges from 2.5% to 10% and the molar ratio of water to carbon ranges from 1.0 to 3.5. The simulation results present species formation characteristics in the reforming reactions which involve only steam reforming reaction and partial reforming reaction. Higher mass ratio of water to fuel (W/F) is advantageous for the methane reforming reaction, more hydrogen yield and the inhibition of the coke formation, while higher EGR ratio promotes the conversion of methane and carbon monoxide production. The simulation result also gets a high molar ratio of hydrogen to carbon monoxide ratio for the presence of excess water content. In the given conditions, a more preferable reaction process can be achieved when EGR rate is equal to 5% and W/F gets the value of 3.5.

Combustion and emission characteristics of DI diesel engine fuelled by ethanol injected into the exhaust manifold

Dual fuel diesel engine operation is an important technique used for combustion control in diesel engines. In this study, ethanol is injected into the exhaust manifold of a single cylinder diesel engine. The exhaust valve opens during the intake stroke, enabling vaporized ethanol to enter the cylinder where it is then ignited by diesel fuel injection. The effects of exhaust gas recirculation (EGR) ratios, ethanol injection timing, and ethanol amount are studied. Furthermore, exhaust and intake manifold injection of ethanol compared under the same conditions. These results reveal that ethanol injection into the exhaust manifold increases the apparent heat release rate (AHRR) at the premixed combustion phase. Additionally, the ignition delay increases with ethanol injection by 0.2° crank angle (CA). The indicated mean effective pressure (IMEP) and total heat released per cycle are increased by 8.2% and 14.2%, while the NOx and soot concentrations are reduced by 88% and 30%, respectively. When compared with exhaust manifold ethanol injection, intake manifold injection results in higher AHRR in the premixed combustion phase, decreased engine performance, an increase in soot production of approximately 35%, and decrease in NOx of 13%.