Exhaust Gas Recirculation Addition Research Articles

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.

Effects of exhaust gas recirculation on nitrogen oxides, brake torque and efficiency in a hydrogen direct injection spark ignition engine

This study investigated the effects of exhaust gas recirculation (EGR) on emission and efficiency in a hydrogen direct injection spark ignition engine. EGR was supplied as the low-pressure (LP)-EGR system by controlling EGR valve from zero to 18.7% in terms of mass fraction. The result showed that EGR effect on nitrogen oxides (NOx) reduction became enlarged as higher engine speed due to increasing residual gas fraction. Also, under the same excessive air ratio (λ:2.2), EGR addition made NOx reduction from 89.9 to 98.7 % as varying engine speed. As NOx limit was low, the maximum brake torque was also reduced. However, by using appropriate EGR, NOx margin could be converted to increasing brake torque under the same NOx concentration level from 1.9% to 18.2% as varying engine speeds. From this result, to achieve the maximum output when reaching the turbocharger’s limit in a hydrogen engine and effectively reduce nitrogen oxide emissions, it is not only dependent on lean combustion but also effective to incorporate approximately 20% EGR into the operating strategy.

Impact of exhaust gas recirculation and nitric oxide on the autoignition of an oxygenated gasoline: Experiments and kinetic modelling

Exhaust gas recirculation (EGR) and NOx affect the autoignition of gasoline in internal combustion engines. In this work, ignition delay times of an oxygenated gasoline (Euro 6 E10) are investigated with EGR and NOx addition. The experimental data are of interest for gasoline surrogate modeling and for predicting fuel ignition behavior in various engine combustion modes. We studied Euro 6 E10 reactivity with EGR additions of 20 % and 40 % (by mass) doped, in select cases, with high levels of NOx (874, 1501, 3174, and 5568 ppm, by mol%). Experiments were performed in two high-pressure shock tubes (HPSTs) and two rapid compression machines (RCMs) over a wide range of temperature (658–1610 K), equivalence ratio (0.5, 1.0) and at pressures of 20 and 30 bar. Results show that EGR addition inhibits Euro 6 E10 gasoline reactivity in the intermediate- and low-temperature regimes, while it is minimally affected at high-temperatures. In contrast, a strong reactivity-promoting effect of NOx is observed at temperatures greater than 825 K for all equivalence ratios investigated, while an inhibiting effect is seen at lower temperatures with a high doping of NOx (1501 ppm). For fuel-lean cases, where Euro 6/EGR mixtures are sensitized with 3174 – 5568 ppm NOx, a significant reactivity-promoting effect is observed across the entire range of conditions investigated, except at temperatures below 830 K, where the NOx-inhibiting effect dominates. A gasoline surrogate model is developed by combining a detailed gasoline surrogate mechanism with appropriate sub-models and making minor updates. The proposed model captures well the influence of EGR and EGR/NOx on Euro 6 E10 autoignition over the wide range of conditions studied here. Finally, sensitivity analyses were conducted to identify key reactions contributing to the perturbative effects of EGR and EGR/NOx on oxygenated gasoline ignition.

Enhancing performance, reducing emissions, and optimizing combustion in compression ignition engines through hydrogen, nitrogen, and EGR addition: An experimental study

Traditional hydrocarbon-based fuels are known for their emissions of partially burned hydrocarbons, nitrogen oxides, and carbon monoxide. The demand for alternative fuels to replace petroleum-based fossil fuels has been steadily increasing over the past decade due to concerns over air pollution, environmental issues, petroleum production uncertainties, and reducing dependence on petroleum products. In this study, hydrogen, EGR (Exhaust Gas Recirculation), and nitrogen were introduced into COME20 (Corn oil methyl ester) fuel. The addition of nitrogen with 26.64% hydrogen and 20% EGR resulted in a decrease in Brake Thermal Efficiency (BTE) and reduced levels of NOx emissions. Various concentrations of nitrogen (6.66%, 9.99%, and 13.32%) were investigated with 26.64% hydrogen and 20% EGR, and the performance, emission, and combustion parameters were evaluated and compared to COME20 and neat diesel. Notably, when nitrogen was absent (0%) and hydrogen and EGR were present at 26.64% and 20% respectively, an increase in BTE was observed compared to the combinations with nitrogen. The addition of nitrogen led to higher levels of CO and HC emissions compared to COME20 and neat diesel at all loads. However, the addition of any percentage of nitrogen with 26.64% hydrogen and 20% EGR resulted in reduced NOx emissions. Additionally, the study revealed a decline in heat release rate and cylinder pressure with the introduction of nitrogen and EGR alongside hydrogen, in contrast to COME20 and diesel. Finally, increasing quantities of nitrogen led to an increase in the ignition delay period.

Effects of hydrogen and EGR on energy efficiency improvement with ultra low emissions in a common rail direct injection compression ignition engine fueled with dimethyl ether (DME) under HCCI mode

This study deals with enhancing the energy efficiency with ultra-low emissions and extending the operating range (maximum load limit) of dimethyl ether (DME) fueled homogeneous charge compression ignition (HCCI) engine using hydrogen and exhaust gas recirculation (EGR). In the neat DME mode, the possible maximum load limit with controlled auto-ignition (CAI) was found as 24% (BMEP of 1.67 bar). Beyond 24% load, the knocking was observed with an advanced combustion phase, and shortened combustion duration resulted in uncontrolled auto-ignition (UAI) combustion. The addition of EGR extended the maximum load limit to 52% (BMEP of 3.62 bar) (60% EGR). Near-zero levels of NOx, zero smoke, and marginal CO and HC emissions reduction were observed with the optimized EGR rate (35%). The hydrogen fuel addition along with DME at an optimized EGR rate resulted in combustion phase retardation with the elimination of the low-temperature reaction (LTR) region. The energy efficiency (EE) and indicated thermal efficiency (ITE) increased along with zero smoke emission, ultra-low NOx, CO, and HC, and lower CO2 emissions till 12% of hydrogen energy share (HES). Thus, the combined strategy of EGR and hydrogen could effectively extend the operating range with ultra-low emissions levels.

The combined effect of EGR and hydrogen addition on a Syzygium cumini (jamun) liquid biofuel engine

Rapid depletion of fossil fuels required the development of alternate and sustainable fuel sources that could replace conventional fuel while having no negative environmental impact. Combining hydrogen induction with biodiesel ensures strict emission standards and lowers energy consumption compared to conventional fuels. In this study, the performance, emissions, and combustion of a CI engine for Syzygiumcumini (B20) were assessed and compared to diesel fuel while using a fixed amount of hydrogen flow rate (6L/m). Throughout the experiment, an exhaust gas recirculation (EGR) technology of 10% and 20% and a constant engine speed of 1500 rpm at varying engine load circumstances were used. When hydrogen is added to B20, it decrease the emissions of carbon monoxide (CO), unburned hydrocarbons (UHC), brake thermal efficiency (BTE), and brake specific energy consumption (BSEC). At maximum load, the use of the EGR system decreased the exhaust gas temperature (EGT) by 13.4% and nitrogen oxide (NOX) emission by 25%, but it had a negative impact on BTE, BSEC, as well as other emission parameters including CO and UHC. Therefore, using hydrogen in dual fuel mode in a CI engine enhances performance and lowers exhaust emissions, while using the EGR approach reduces NOX emissions.

Quantification of φ-operating range with impact of exhaust gas recirculation under low-temperature combustion mode with polyoxymethylene dimethyl ether: A perspective study

Low-Temperature Combustion (LTC) especially Homogeneous charge compression ignition (HCCI) mode of combustion is a capable substitute mode of combustion to conventional diesel combustion (CDC) to provide better soot-NOx trade-off and HC-CO trade-off characteristics. The current study mainly focuses on the Exhaust Gas Recirculation (EGR) effects and equivalence ratio optimization on W20P20 (64% diesel, 16% WCO biodiesel, and 20% PODE) fuel along with exergy analysis in the HCCI mode of operation. The reason for inculcating exergy analysis in this research is to depict that low-temperature combustion provides a better heat transfer rate inside the cylinder. EGR has been varied in terms of 10%, 20%, and 30% in volume proportions along with the inlet fuel-air mixtures since, the fuel was injected through a pilot fuel injector in the inlet manifold. A novel factor in this research is considering both soot-NOx and HC-CO trade-off characteristics in optimizing the equivalence ratio with the influence of EGR over W20P20 fuel. The performance parameters such as BTE and BSEC show a mere decrement of about 6.67% and 29% of maximum with the influence of EGR while better combustion was found in terms of avoiding misfiring at a low equivalence ratio of 0.29–0.35 and knocking at a high equivalence ratio of 0.61–0.71 for W20P20 fuel. The operating range extension of the equivalence ratio was found with W20P20 fuel which further increased again with the increase in EGR addition. The emission limits of soot, NOx, CO, and HC particles were analyzed, in which the highest NOx reduction of 53% was obtained with 30% EGR irrespective of the equivalence ratio. The highest soot reduction was 61.85% with 20% EGR at a higher equivalence ratio. The highest HC reduction was 18% with 20% EGR at a lower equivalence ratio. The CO emissions seemed to reduce by 12% at a lower equivalence ratio while they increased by 47% at a higher equivalence ratio. The comparative results were studied for EGR influence with W20P20 fuel in the HCCI mode of combustion.

A Numerical Study on the Combustion and Emissions Characteristics of a Heavy Duty Natural Gas/Diesel RCCI Engine

Abstract Due to energy shortages and environmental issues, the application of reactivity controlled compression ignition (RCCI) combustion in internal combustion engines has received extensive attention. Through the verification of the model, RCCI combustion can be accurately simulated. In this study, the combustion and the emission performance of a single-cylinder heavy-duty natural gas/diesel RCCI engine have been optimized through numerical simulation. Six important parameters including start of injection (SOI) timing, intake valve closing temperature, intake valve closing pressure, exhaust gas recirculation (EGR), swirl ratio, and spray angle have been investigated. The goal is to meet the requirements of European VI emission regulations while maintaining a high gross indicated efficiency (GIE). A strategy to achieve clean and efficient combustion of RCCI engine is proposed. The results showed that the addition of EGR can effectively reduce nitrogen oxide (NOx) emissions. SOI had the greatest impact on RCCI combustion and emission performance. Earlier SOI can improve the uniformity of the fuel mixture in the cylinder. Under the combined optimization of six important parameters, NOx, hydrocarbons, and carbon monoxide emissions can meet European VI emission regulations, and fuel consumption can meet Environmental Protection Agency consumption regulations, improving the GIE.

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.

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.

Assessment on Performance and Emission Characteristics of the CRDI Engine Fueled with Ethanol/Diesel Blends in Addition to EGR

In this research, the CRDI engine characteristics were analyzed with the aid of exhaust gas recirculation rate (EGR) adoption fueled with ethanol blends. The test fuels were the various blends with ethanol, such as (10% of ethanol + 90% of diesel) E10D90 (20% of ethanol + 80% of diesel), E20D80, and (30% of ethanol + 70% of diesel) E30D70. From the results, it was revealed that performance characteristics were reduced when using a higher concentration of the alcohols mixed with diesel fuel. The blend E30D70 showed that brake thermal efficiency (BTE) without EGR drops by 3.8%, increased by 9.14% of BSFC, a 9.25% decrease in oxides of nitrogen emissions, and slightly decreased CO and HC emissions compared to baseline diesel operation at 60% load condition. The blend E10D90 with 20% EGR shows the highest BTE of 8.87% when compared with base fuel, due to proper fuel mixture taking place in the inlet manifold. The results indicate that the engine runs smoothly, and E30D70 has chosen an optimum blend. A further experiment was performed using E30D70 with different rates of exhaust gas recirculation system. The addition of exhaust gas recirculation with E30D70 in the common rail diesel engine exhibits oxides of nitrogen emission, but in contrast, it was noticed to have inferior performance characteristics and drastically decreased HC and CO emissions. The hydrocarbon emission decreased E10D90, E20D80, and E30D70 at 60% load condition by 21.42%, 37.38%, and 48.76%, respectively. The blends E10D90, E20D80, and E30D70 decreased carbon dioxide by 7.9%, 30.08%, and 31.98%, respectively. The maximum reduction of NOx emission was observed at about 51.06% at an EGR rate of 20% with E30D70.

Impacts of using EGR and different DI-fuels on RCCI engine emissions, performance, and combustion characteristics

• EGR contributed to further reductions in NOx emissions in RCCI combustion. • Improvements in BTE and BSFC were achieved by using EGR in RCCI combustion. • Better RCCI operation with EGR requires an alternating premixed fraction. • Increased biodiesel dose in DI-Fuel lead to an increment in NOx emissions. Exhaust gas recirculation (EGR) seems to be a critical parameter in developed RCCI operations for controlling emissions, in-cylinder charge reactivity as well as combustion phasing. The most advantages of utilizing the RCCI burning technique are the simultaneous decrease of PM as well as NOx emissions. Nevertheless, significant challenges remain, such as extreme HC and CO emissions. The purpose of this work is to investigate the effects of external, hot, and high-pressure EGR as well as different DI-Fuels on RCCI combustion under various load conditions. The tests were performed on direct injection, single-cylinder, and four-stroke modified diesel engine (peak power 5 KW under 1500 rpm) operating in RCCI mode with an EGR system. To initiate ignition, high reactivity fuel (biodiesel/diesel blends) was injected directly inside the engine's cylinder whereas low reactivity fuel (LPG) was induced into to intake mixing chamber. EGR at various ratios (30%, 20%, and 10%) was introduced into the engine via the intake mixing chamber, and experiments were done under various loads. The results show that increasing EGR results in a slight increment in BTE under medium and high engine loads. NOx emissions from diesel engines operating in traditional RCCI mode declined dramatically, and they decreased even further with the addition of EGR. The CO and HC emission levels, on the other hand, are slightly greater when EGR is used. Increasing the proportion of biodiesel in DI-Fuel is resulting in a decrement in BTE and NOx emissions in addition to an increment in BSFC, CO, and HC emissions.

Assessment of Diesel Engine Performance, Combustion and Emission Characteristics with Supplementation of Neem Oil Methyl Ester Along With EGR

Biodiesel generated from a variety of non-edible feedstocks has gained widespread acceptance as a limited diesel fuel alternative in compression ignition engines. For the reliable implementation of biodiesel in commercial sectors, its effect on engine combustion, emission, and performance needs to be examined experimentally. In this study, 10% (N10) and 20 % (N20) Neem oil methyl ester (NME) blends were tested in a direct injection 4-stroke single-cylinder diesel engine incorporated with 5% and 10% exhaust gas recirculation (EGR). At maximum load conditions, Brake thermal efficiency (BTE) was found highest for N20 by 7.2%, and also Brake specific energy consumption (BSEC) was reduced by 11.4% for N20 as compared to diesel. Meanwhile, the incorporation of EGR deteriorates the performance parameters for the N20 blend. The results of emission analysis showed that oxides of nitrogen (NOx) increased with the addition of biodiesel whereas the addition of EGR diminished the NOx value for both biodiesel blends at all loading conditions. Unburnt hydrocarbon (UHC), Carbon monoxide (CO), and smoke emissions decreased by 40.6%, 31.2%, and 29.6% for the N20 blend respectively at full load when compared to diesel. Interestingly, when EGR was provided, CO, UHC, and smoke density values are increased for both N10 and N20 blends at all loading conditions, however lower than diesel operation.

Filtration Efficiency and Regeneration Behavior in a Catalytic Diesel Particulate Filter with the Use of Diesel/Polyoxymethylene Dimethyl Ether Mixture

Polyoxymethylene dimethyl ether (PODEn) is a promising diesel additive, especially in particulate matter reduction. However, how PODEn addition affects the filtration efficiency and regeneration process of a catalytic diesel particulate filter (cDPF) is still unknown. Therefore, this experimental work investigated the size-dependent particulate number removal efficiency under various engine loads and exhaust gas recirculation (EGR) ratios when fueling with diesel (D100) and diesel/PODEn mixture (P10). In addition, the regeneration behavior of the cDPF was studied by determining the breakeven temperatures (BETs) for both tested fuels. The results showed that the cDPF had lower removal efficiencies in nucleation mode particles but higher filtration efficiencies in accumulation mode particles. In addition, the overall filtration efficiency for P10 particles was higher than that for D100 particles. Positioning the upstream cDPF, increasing the EGR ratio slightly decreased the number concentration of nucleation mode particles but greatly increased that of accumulation mode particles. However, increasing the EGR ratio decreased the removal efficiency of nanoparticles, and this effect was more apparent for the P10 case. Under the same period of soot loading, the pressure drop of P10 fuel was significantly lower than that of diesel fuel. In addition, a significantly lower BET was observed for the P10 fuel, in comparison with D100 fuel. In conclusion, adopting cDPF is beneficial for fueling with P10 in terms of the overall filtration efficiency in the particulate number and the lower input energy requirement for active regeneration. However, with the addition of EGR, the lower filtration efficiencies of nanoparticles should be concerned, especially fueling with diesel/PODEn mixture.

An experimental study on the effect of injection pressure on diesel PCCI engine

The aim of this work was to analyze the effects of injection pressure and exhaust gas recirculation (EGR) on combustion, performance, and emissions characteristics of diesel premixed charge compression ignition (PCCI) mode. In this work, the injection pressure of diesel was varied from 500 bar to 1000 bar. The optimum injection pressure in diesel PCCI mode was identified based on the engine performance and emissions. The thermal efficiency was improved and smoke emission was drastically reduced as increasing injection pressure. However, injection pressure was not significantly influence the amount of NO, HC and CO emissions. The diesel PCCI mode was possible until a brake mean effective pressure (BMEP) of 2 bar since there was a vigorous knocking at higher BMEPs. Addition of EGR retarded the combustion process, suppressed the knocking, increased the thermal efficiency and extended the operating range to higher BMEPs of 3 and 4 bar.

Knock analysis of bio-butanol in TISI engine based on chemical reaction kinetics

The knocking combustion of n-butanol (bio-butanol) combined with exhaust gas recirculation (EGR) in turbocharge direct injection spark ignition (TISI) engine with high compression ratio is studied. Mainly analyze the influence of EGR rate and composition on knock combustion and the indication effect of unconventional emission of free radicals on knock. The research results show that adding appropriate EGR can reduce the engine knock intensity, but the introduction of a large amount of EGR can cause the knock intensity to increase. When the EGR rate is 8%, the MAPO is less than 0.1 MPa, indicating that knocking combustion does not occur in the cylinder. When the EGR rate is increased to 15%, the MAPO is greater than 0.15 MPa, indicating that knocking combustion is intensified. Knock combustion is mainly concentrated on the intake side, which is related to the flame propagation speed. The addition of EGR can reduce the temperature in the cylinder, mainly because the specific heat capacity of H2O and CO2 in the EGR component is relatively large, which can significantly reduce the temperature of the mixture. The variation of CH2O, CH3CHO and C2H4 can reflect the knock intensity of the mixture in the cylinder. In conclusion, the introduction of EGR into the TISI engine can effectively reduce the knock intensity. The variation of mixture composition can better reflect the knock region and knock intensity.

Hydrogen-diesel co-combustion characteristics, vibro-acoustics and unregulated emissions in EGR assisted dual fuel engine

This work investigates the co-combustion characteristics of the hydrogen-diesel dual fuel with exhaust gas recirculation (EGR). The experiments were performed on a retrofitted duel fuel compression ignition engine for the entire engine load spectra, while the maximum hydrogen energy share in the study was 30%. Further, EGR was varied up to 10% to examine its effect on the hydrogen-diesel co-combustion and other relevant characteristics. It was found that although, hydrogen exhibit contrasting effects on the combustion at low and high loads, EGR continually degraded the peak combustion pressure. However, interestingly, the combustion’s variability improved on addition of EGR at higher loads, despite EGR’s detrimental effect on variability at lower loads. In addition, combustion noise and engine vibration were also studied with the aim to understand the effect of fuels and their combustion stability on such parameters. The relatively lower participation of hydrogen tends to reduce the vibrations, however, EGR leads to higher vibrations in the engine. The combustion noise however reduced with addition of hydrogen and EGR at lower loads. Further, the cumulative effect of EGR- hydrogen on the much unattended but harmful unregulated emissions was also investigated, and a synergy between the hydrogen addition and EGR was observed in this study. The present study showcases the key concerns as well as advantages in the EGR assisted hydrogen diesel combustion.

Lean flammability limit of high-dilution spark ignition with ethanol, propanol, and butanol

Ethanol, n-propanol, isopropanol, n-butanol, isobutanol, and sec-butanol are six potential carbon-neutral fuels of the future. One application of these carbon-neutral fuels is in high-dilution spark ignition. To understand the potential of these fuels in high-dilution spark ignition, this work experimentally determines the spark ignition lean flammability limit of each fuel with no external, cooled exhaust gas recirculation (EGR), and with 20% external, EGR. The spark ignition lean flammability limit in this work is defined as the excess-air ratio that results in a coefficient of variance of gross indicated mean effective pressure greater than 5%. This is done on an engine with a compression ratio of 12.5, using an intake pressure of 1 bar and an intake temperature of 320 K. It was found that ethanol had the leanest lean limit, due to its high flame speed, followed by n-propanol, isopropanol, and sec-butanol, which all had similar lean limits. n-Butanol and isobutanol had the richest lean limits due their high knock propensity and low flame speed, respectively. The lean limit of each fuel decreased with external, cooled EGR addition, with ethanol as the least sensitive and isopropanol as the most sensitive to EGR addition. Overall, using a high dilution strategy increased the cycle efficiency for each fuel. Ethanol, n-propanol, isopropanol, and sec-butanol all showed promising performance and are great candidates to be combined with an advanced high-dilution SI strategy to enable high-dilution SI with a carbon-neutral fuel.

Properties and oxidation of in-cylinder soot associated with exhaust gas recirculation (EGR) in diesel engines

The properties and oxidation of in-cylinder soot from a diesel engine fueled with n-heptane were explored under the simulated exhaust gas recirculation (EGR) condition, via CO2 addition to the intake air of the engine. A self-developed total cylinder sampling system was employed to obtain the soot samples at the EGR ratios of 0 and 25%, and this study only focused on the soot oxidation that occurred in the soot oxidation-dominated (SOD) phase. Computational fluid dynamics (CFD) simulations were performed to determine the local combustion characteristics related to soot oxidation. Soot oxidation rates were evaluated based on in-cylinder soot mass traces and CFD results. Soot properties were characterized in terms of nanostructure, carbon chemical state, and surface functional groups. Detailed analysis of the soot mass indicates that EGR addition enhances the mass-based specific rate of soot oxidation. However, CFD results show that EGR addition reduces the flame temperature and the concentrations of O2 and OH, and consequently decreases soot surface oxidation rates by O2 and by OH. The characterization of soot properties shows that EGR decreases the degree of structural ordering and results in the formation of more oxygenated and aliphatic C–H groups on the soot surface. This alteration in physico-chemical properties favors soot oxidation during the combustion process, and results in an increase in the mass-based specific rate of soot oxidation in the SOD phase.

Experimental investigation and numerical assessment the effects of EGR and hydrogen addition strategies on performance, energy and exergy characteristics of a heavy-duty lean-burn NGSI engine

In order to investigate the influences of hydrogen addition and exhaust gas recirculation (EGR) strategies on performance, combustion, emissions, energy and exergy balance of a lean-burn and high compression ratio (CR) (13.6) natural gas spark ignition (NGSI) engine fueled with 99% methane content is tested on the engine bench under different hydrogen contents. A corresponding 1D GT-Power simulation model is built and validated according to experimental data. In the first stage, both peak cylinder pressure (PCP) and peak heat release rate (HRR) increase with the hydrogen addition but decrease with increased EGR ratio. Besides, EGR addition will retard the effect of various hydrogen contents on performance and combustion of the engine. In the second stage, the NOx emissions increase with hydrogen enrichment but decrease with the increase of EGR rate due to the variation of in-cylinder temperature, which emphasizes effective method of EGR addition strategies to reduce the NOx emissions on the lean-burn NGSI engine fueled with natural gas-hydrogen (HNG). Finally, the change trends of exergy terms are similar to their corresponding energy, but the percentages of heat transfer exergy and exhaust exergy are about 7.05 and 2.61 times lower than their corresponding energy. Furthermore, the simulation model and data in the paper can be applied to evaluate and optimize the energy distribution and performance by changing different technologies, strategies and fuels in the future. What is more, the analysis of the energy and exergy balance can provide a new thought for the future research to improve engine’s performance.