Increasing Exhaust Gas Recirculation Rate Research Articles

Effect of exhaust gas recirculation(EGR) on combustion and emission of butanol/gasoline combined injection engine

N-butanol is a kind of biomass alcohol which can be produced by fermentation, and it is also a clean alternative fuel. The combustion and emissions characteristics of n-butanol/gasoline SI engine under different combined injection modes with the introduction of EGR was studied. N-butanol inlet injection plus gasoline in-cylinder direct injection is called N-GXDI; Gasoline inlet injection plus n-butanol in-cylinder direct injection is called G-NXDI. Through the analysis of combustion and emission performance under different EGR rates, injection modes and direct injection ratios (DIr), it is found that with the increase of DIr, cylinder temperature, pressure, and IMEP increase first and then decrease. Under the DIr = 50%, the combustion is more complete when the EGR rate is 5%. Under the same DIr, with the increase of EGR rate, CO emission decreased first and then increased, NOx emission opposite, THC emission increased. Under the same EGR rate, the total particle number of the two modes decreases first and then increases with the increase of DIr. The G-NXDI mode has advantages in combustion and primary emissions, while the N-GXDI mode has advantages in particulate emissions, suitable injection mode combined with EGR can greatly improve combustion and emission performance.

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.

Numerical study of effect of post injection coupled with EGR on combustion and emission performances of CRDI engine fueled with biodiesel-ethanol blends

Energy shortage and environmental pollution are becoming more serious, biodiesel is regarded as the most promising alternative fuel for diesel engines due to its environmentally friendly and renewable characteristics. In this study, the biodiesel-ethanol blends were used in a diesel engine, and the purpose of the study was to simultaneously control the NOx and soot emissions of the diesel engine by adjusting the injection strategy and EGR rate. A turbocharged, six-cylinder, common rail direct injection (CRDI) engine model was established using GT-Power. The effects of the main-post injection strategy and post injection coupled with exhaust gas recirculation (EGR) on combustion and emission characteristics were investigated at a maximum torque speed and a medium load. The results show that when the main-post injection strategy is employed, the combustion duration of the main injection is shortened with an increase in the main-post injection interval (MPI). When the MPI increased to more than 18 °CA, the heat release of post injection could be observed clearly from the curve of the heat release rate, NOx emissions decreased by 5.70% and 7.12%, respectively, and soot emissions decreased by 25.56% and 30.20%, respectively. Moreover, with the increasing post injection quantity, the combustion duration of the main injection shortened, and the peak heat release rate (PHRR) of the post injection increased. When the fuel quantity for the post injection increased from 2 to 6 mg, NOx emissions decreased from 2.33% to 9.80%, and soot emissions decreased from 16.10% to 34.97%. The effect of post injection quantity on emissions was more significant than that of the MPI. In addition, with increasing EGR rate, the ignition delay is prolonged, the peak cylinder pressure, PHRR, peak combustion temperature and NOx emissions decrease, whereas soot emissions increase gradually. Main-post injection can improve the NOx-soot trade-off, the optimal EGR rate is 22.86% under a post injection quantity of 4 mg and a MPI of 22 °CA.

Numerical study on the effect of the combustion system parameters on combustion and emission characteristics for a HPDI natural gas/diesel dual fuel engine

Replacing diesel by natural gas in diesel engine is of great interest for transportation and power station industry due to larger availability and lower environmental impact of natural gas compared to diesel fuel. In addition, the high-pressure direct injection (HPDI) natural gas engine is widely recognized as a positive development prospect and an ideal alternative to conventional diesel engine. However, the trade-off relationship between indicated thermal efficiency (ITE) and NOx emissions limits the development of dual-fuel engines. In order to resolve this problem, we established a three-dimensional model combined with a multicomponent reduced chemical kinetic model and a phenomenological soot model. Using the 3D simulation model, we jointly optimized the combustion chamber (CC) structure, diesel/natural gas (NG) injection pressure (IP), and exhaust gas recirculation (EGR) strategy for HPDI NG engine in the two combustion modes. The results show that the adoption of the straight crater type (SCT) CC improves the mixture space equivalent ratio gradient distribution, slightly increases NOx emissions, rises ITE and reduces CO emissions in the two combustion modes. In NG mixture-limited combustion (NMLC) mode, increasing the diesel injection pressure (DIP) while appropriately increasing the NG injection pressure (NIP) promotes multi-point ignition and faster flame propagation and further optimizes CO emissions. In NG slightly premixed combustion (NSPC) mode, high ITE and low CO emissions can be maintained by increasing DIP while slightly increasing NIP, but the NOx increases substantially. In the moderate NOx emissions region (1.0 g/kW·h ∼ 2.0 g/kW·h), as the EGR rate increases, an overall improvement in trade-off relationships of NOx-CO, NOx-soot, and NOx-ITE in NMLC mode can be achieved. In NSPC mode, as the EGR rate increases, although CO and soot emissions can maintain lower values, it is difficult to improve the trade-off relationship of NOx-ITE.

Numerical study on effects of EGR on combustion and NOx emissions of gasoline blended dissociated methanol gas engine

Exhaust gas recirculation (EGR), which can reduce NOx emissions effectively, has been widely studied in engines, but there are few studies using EGR on gasoline blended dissociated methanol gas (GDM) engines. To reduce the NOx emissions of GDM engines, investigation is conducted based on numerical simulation in this study. The accuracy of the engine numerical model is first validated through experimental data, and then the effects of EGR on GDM engine performance are studied, including combustion characteristics and NOx emissions. Numerical simulation results show that the application of EGR reduces the cylinder pressure and the heat release rate of GDM engine, and delays the corresponding crank angle of their peak value respectively. The application of EGR also delays the combustion center, and extends the ignition delay and combustion duration. As EGR rate increases, the NOx emissions decrease significantly. This study offers valuable insights into the potential application of EGR technology in GDM engines.

Study on the Effects of the Hydrogen Substitution Rate on the Performance of a Hydrogen–Diesel Dual-Fuel Engine under Different Loads

Due to having zero carbon emissions and renewable advantages, hydrogen has great prospects as a renewable form of alternate energy. Engine load and hydrogen substitution rate have a considerable influence on a hydrogen–diesel dual-fuel engine’s efficiency. This experiment’s objective is to study the influence of hydrogen substitution rate on engine combustion and emission under different loads and to study the impact of exhaust gas recirculation (EGR) technology or main injection timing on the engine’s capability under high load and high hydrogen substitution rate. The range of the maximum hydrogen substitution rate was determined under different loads (30%~90%) at 1800 rpm and, then, the effects of the EGR rate (0%~15%) and main injection timing (−8 °CA ATDC~0 °CA ATDC) on the engine performance under 90% high load were studied. The research results show that the larger the load, the smaller the maximum hydrogen substitution rate that can be added to the dual-fuel engine. Under each load, with the increase of the hydrogen substitution rate, the cylinder pressure and the peak heat release rate (HRR) increase, the equivalent brake-specific fuel consumption (BSFCequ) decreases, the thermal efficiency increases, the maximum thermal efficiency is 43.1%, the carbon dioxide (CO2) emission is effectively reduced by 35.2%, and the nitrogen oxide (NOx) emission decreases at medium and low loads, and the maximum increase rate is 20.1% at 90% load. Under high load, with the increase of EGR rate or the delay of main injection timing, the problem of NOx emission increases after hydrogen doping can be effectively solved. As the EGR rate rises from 0% to 15%, the maximum reduction of NOx is 63.1% and, with the delay of main injection timing from −8 °CA ATDC to 0 °CA ATDC, the maximum reduction of NOx is 44.5%.

Optical diagnostic study of internal and external EGR combined with oxygenated fuels of n-butanol, PODE3 and DMC to optimize the combustion process of FT synthetic diesel

With the introduction of carbon neutrality target, Fischer-Tropsch (FT) synthetic fuels are coming back into the limelight as a kind of carbon–neutral fuel. However, the mismatch between the overly high cetane number (CN) and the relatively low vaporability of FT synthetic diesel is unfavorable to the soot emission control, which will make it difficult to meet more stringent fuel consumption and emission regulations in future applications. To investigate the potential of oxygenated fuels combined with different exhaust gas recirculation (EGR) introduction schemes to achieve high-efficiency and clean combustion of FT synthetic diesel, an optical diagnostic study was carried out based on high-speed photography and the two-color method. The results show that all three kinds of oxygenated fuels could suppress soot emissions via self-carrying oxygen and adjusting the physicochemical properties of the fuel blend. Compared with the combustion characteristics of FT synthetic diesel, the flame area and luminosity of oxygenated blends are reduced, and the in-cylinder temperature and soot KL factor are lowered. Among them, n-butanol exhibits a greater capability of soot control compared to polyoxymethylene dimethyl ethers (PODE3) and dimethyl carbonate (DMC). In addition, introducing internal and external EGR to the engine fueled by n-butanol/FT synthetic diesel blend shows that with the increase of EGR rate, the external EGR exhibits a gradually stronger inhibiting effect on the heat release process and soot KL factor, while the internal EGR exhibits an inhibiting and then promoting effect. Moreover, the high ratio internal EGR shortens the ignition delay (ID) significantly due to the strong heating effect, which is unfavorable to the control of soot emission. The combination of oxygenated fuels and internal/external EGR could effectively optimize the combustion process of FT synthetic diesel and inhibit soot generation, but the EGR rate needs to be controlled within a proper range.

Influence of the low-pressure exhaust gas recirculation injection point on engine performance

The use of low-pressure exhaust gas recirculation (EGR) has been extended in spark-ignited engines in recent years due to advantages from efficiency perspective. However, the potential condensation of the water contained in the exhaust gases and eventual compressor erosion can limit the usage of such systems during engine warm-up and/or cold ambient conditions. One possibility to avoid condensation at cold ambient is to place the EGR injection close to the compressor wheel, avoiding a complete mixture of both streams, but it alters the flow distribution upstream of the compressor, potentially affecting its performance. In order to assess the impact of this phenomenon in engine operation, a detailed experimental campaign in a state-of-the-art spark-ignition engine was performed comparing this close-coupled configuration with another one where the injection point was far upstream the compressor, ensuring a perfect mixing. A previously developed and validated one-dimensional model of the variable geometry turbocharger was used to analyze in further detail the compressor and turbine operation. The results show a general deterioration of the engine pumping mean effective pressure (up to 0.02 bar) and the specific fuel consumption (up to 4 g/kWh) when applying the close configuration, higher as the EGR rate increases, which is partially due to the change in turbine operation induced by the new compressor working point.

Experimental study of gasoline engine with EGR dilution based on reactivity controlled turbulent jet ignition (RCTJI)

The exhaust gas recirculation (EGR) method can suppress knock and improve the thermal efficiency of engines, but it also deteriorates the combustion stability and engine power. Turbulent jet ignition (TJI) is a reliable ignition way for improving ignition stability and burning rate. However, the EGR in the pre-chamber will worsen the reactivity of the fuel-air mixture in the pre-chamber and subsequently lower the intensity of the TJI. To this end, the reactivity controlled turbulent jet ignition (RCTJI) based on a newly air-assisted pre-chamber turbulent jet ignition with a scavenging function has been proposed to improve the reactivity in the pre-chamber for the first time. The combustion characteristics, pressure oscillation, and combustion stability of a single-cylinder spark-ignition engine under four ignition modes of spark ignition (SI), passive TJI, active TJI, and scavenged TJI have been investigated. The results show that three TJI modes can obviously shorten the combustion duration due to the fast jet flame. Compared to the SI mode, the spark timing of TJI is not sensitive to the change in EGR rate. In particular, the scavenged TJI could effectively promote the chemical reactivity in the pre-chamber, and subsequently improves the intensity of the turbulent jet flame and shortens the ignition delay and combustion duration. As a result, using the scavenged TJI can effectively reduce cycle variation and achieve the lowest indicated specific fuel consumption (ISFC) at high EGR rates. However, with the increase in EGR rate, the SI combustion gradually becomes unstable. In contrast, the scavenged TJI can effectively extend the EGR tolerance. In addition, the present work further has confirmed the three main combustion stages of jet ignition in terms of the heat release rate.

Effects of EGR combined with DOC on emission characteristics of a two-stage injected Fischer-Tropsch diesel/methanol dual-fuel engine

Fischer-Tropsch (F-T) diesel and methanol are widely regarded as promising clean alternative fuels for engines. The emergence of reactivity controlled compression ignition (RCCI) combustion mode provides new approaches to the application of F-T diesel and methanol in diesel engines, but there is a pressing need to further reduce engine emissions. To this end, a dual-fuel engine test bench was built based on a high-pressure common rail diesel engine with a methanol injection system at the intake manifold combined with a two-stage in-cylinder direct injection (pre-injection + main injection) F-T diesel. The combined effects of methanol substitution ratio (MSR), exhaust gas recirculation (EGR) and diesel oxidation catalyst (DOC) on the combustion and emission characteristics of the dual-fuel engine was investigated at 2000 rpm and 75 % load. The results show that EGR improves the combustion characteristics of the F-T diesel/methanol dual-fuel engine while adding a DOC significantly reduces engine gaseous emissions. However, as the MSR and EGR rate increase, NOx emissions decrease, but other emissions increase. NOx emissions were reduced by 73 % compared to the original engine emissions for an MSR of 30 % and an EGR rate of 15 % without a DOC. When the MSR is 0 %, the DOC promotes the conversion of NO to NO2. While, when the MSR greater than 0, the DOC promotes the conversion of NO2 to NO. When equipped with a DOC, CO, NO, NO2, NOx, MeOH, and HCHO emissions decrease as the EGR rate increases, with the reduction of CO and MeOH emissions being greater than 99.5 % and 93 %, respectively, and the maximum conversion efficiency for HCHO emissions being 82 %. The present study showcases the key challenges as well as advantages in the use of EGR combined with a DOC assisting the application of coal-based alternative fuels in dual-fuel engines.

Effect of brown gas (HHO) addition on combustion and emission in gasoline engine with exhaust gas recirculation (EGR) and gasoline direct injection

As a hydrogen-based fuel that can be used immediately after generation without storage, brown gas (HHO) has important research significance and practical development prospect. In this paper, the exhaust gas recirculation (EGR) and lean-burn of gasoline direct injection (GDI) engine blended with HHO are studied. The effects of different HHO flux, λ and EGR rate on engine performance were studied experimentally. The results show that peak in-cylinder pressure (Pmax), Torque and its best EGR rate increases with the increase of HHO flux. When λ is 1, EGR is 18%, HHO flux is 16L/min, Torque reaches the maximum 53.47N·m. coefficient of indicated mean effective pressure variation (CoVIMEP), crank angle corresponding to Pmax (APmax), ignition delay period (CA 0–10) and rapid combustion period (CA 10–90) decreases with the increase of HHO flux. When λ is 1.2, EGR is 18%, HHO flux increases from 0 to 16L/min, the maximum reduction of CA 0–10 and CA 10–90 is 27.36% and 34.41%. Under lean-burn conditions, IMEP increases first and then decreases with the increase of HHO flux and EGR rate; when λ is 1.1, EGR is 12%，HHO flux is 16L/min, IMEP reaches the maximum value of 4.23 bar; when HHO flux is 16L/min, EGR is greater than or equal to 6% and less than or equal to less than or equal to 12%, both Pmax and APmax are at the best level. Carbon monoxide (CO) and hydrocarbon (HC) on the whole decreases with the increase of HHO flux. And when HHO is 16L/min, EGR less than 6%, CO and HC always at a low level. nitric oxide (NO) increases with the increase of HHO flux. under three λ conditions, when HHO flux is 16L/min and EGR rate increases from 0% to 18%, NO can still be reduced by 79.36%, 87.98% and 87.56%%, respectively. In general, GDI add HHO add EGR mode can effectively improve the combustion and emission characteristics of the gasoline engine, especially in the lean-burn condition. And 16L/min HHO and 6% ≤ EGR ≤ 12% is the optimal combination.

Numerical Study on the Effects of Pilot Diesel Quantity Coupling EGR in a High Pressure Direct Injected Natural Gas Engine

ABSTRACT The natural gas high pressure direct injection (HPDI) engines have attracted attention due to their high combustion stability and thermal efficiency comparable to diesel. However, the nitrogen oxides (NOx) emissions from HPDI engines remain high. In this study, the coupling effects of the exhaust gas recirculation (EGR) and pilot diesel quantity were investigated on a four stroke HPDI engine by simulation. Three pilot diesel quantities and four EGR rates were involved, and the combustion and emission characteristics of the engine were compared and discussed. The results show that with increasing EGR rate, the maximum combustion pressure (Pmax) decreases with different pilot diesel quantity, and the crank angle corresponding to the maximum combustion pressure (CPmax), the crank angle corresponding to the maximum heat release rate (CHRRmax) and the crank angle corresponding to the 50% cumulative heat release (CA50) are all pushed back. NOx emissions decrease gradually with the increase of EGR rate, but soot, unburned hydrocarbon (HC) and carbon monoxide (CO) emissions and methane escape all increase and the indicated thermal efficiency (ITE) decreases. The traditional “trade-off” relationship between NOx and soot emissions still exists on HPDI engine and becomes more obvious as the quantity of pilot diesel increases. NOx and soot emissions can be well balanced at moderate EGR rate. Increasing the quantity of pilot diesel can partially offset the hysteresis effect of EGR on the combustion process. And when the EGR rate is controlled within 30%, increasing the quantity of pilot diesel is beneficial to reduce HC and CO emissions and methane escape. By increasing the quantity of pilot diesel coupled with a moderate level of EGR rate, it is possible to significantly reduce NOx emissions while maintaining the ITE, methane escape and unburned diesel, HC and CO emissions at the same level as without EGR. But soot emissions will increase substantially.

Experimental analysis of the EGR rate and temperature impact on combustion and emissions characteristics in a heavy-duty NG engine

Cooled exhaust gas recirculation (EGR) is one of the most effective methods in spark ignition (SI) natural gas (NG) engines to improve the fuel economy and reduce the nitrogen oxides (NOx) emissions. The objective of this study is to anatomize the EGR rate and temperature impact on the combustion and emissions characteristics by the experiments in a heavy duty (HD) NG engine under various spark timings. The results showed that the increasing EGR rate reduced the burning rate and extended the combustion duration. Spark timing should be optimized to copy with the retarded combustion phase. Under high EGR rate, the combustion performance could be optimized with the increase of EGR temperature. There exists a proper EGR rate in real application for the fuel consumption of the engine. Higher EGR temperature plays positive effects on fuel economy, owing to the higher combustion efficiency and lower throttle losses, and the decreasing amplitude of BSFC is 1.25% between the EGR temperatures of 333 K and 373 K. With the increase of EGR rate from 5% to 25%, NOx emissions are reduced by up to 76%, the unburned hydrocarbon (HC) and carbon monoxide (CO) emissions are increased by 34.6% and 12.9% respectively. Higher EGR temperature could alleviate the increase of HC and CO emissions, but sacrificing the NOx emissions, and the increase extent of NOx emissions is 35.3%. The results provide an insight into the quantitative comparisons of EGR rate and temperature on the NG engine performance and emissions, which promotes the utilizing EGR strategy in SI NG engines.

Experimental study of effects of exhaust gas recirculation and combustion mode on combustion, emission, and performance of DME‐methanol ‐fueled turbocharged c ommon‐rail engine

In this study, the effects of exhaust gas recirculation (EGR) on the combustion, performance, and emission of a six-cylinder turbocharged common-rail dimethyl ether (DME) engine with methanol blends are experimentally investigated, and the proportions of methanol considered are 0% (DME), 5% (M5), 10% (M10), and 15% (M15) by weight. A comparison of direct-injection compression ignition (DICI) combustion and partially premixed charge compression ignition (P-PCCI) combustion is conducted, and P-PCCI combustion is achieved by a two-stage injection. The results indicate that the NOx emissions decrease, but the CO and HC emissions increase approximately linearly as the EGR rate increases. The addition of methanol delays the combustion, shortens the combustion duration, and increases the pressure rise rate. In addition, the NOx emissions decrease, whereas the CO and HC emissions increase significantly as the methanol proportion increases. M5 exhibits the lowest fuel consumption for both the P-PCCI and DICI combustions. Compared to the DICI mode, in the P-PCCI mode, the peak in-cylinder pressure is higher, maximum pressure rise rate is considerably lower, NOx emissions are better suppressed and approximately 20% lower, CO and HC emissions are greater, and particle emission is slightly lower.

Effects of EGR and Alternative Fuels on Homogeneous Charge Compression Ignition (HCCI) Combustion Mode

We present in this article an analysis of the impacts of the exhaust gas recirculation (EGR) and alternative fuels on HCCI combustion mode. The objective is to reduce the pollutant emissions below the levels of established pollution standards. The ANSYS CHEMKIN-Pro software and the combined chemical kinetics mechanism were used to perform simulations for a closed homogeneous reactor under conditions relevant to HCCI engines. The calculation process is based on one single-zone in the combustion chamber. Numerical simulation has proven the ability of the models adopted, which use the essential mechanisms of the fuel combustion process, to reproduce, among other things, the evolution of the formation of chemical species. This study showed that adding hydrogen (H2) to methane (CH4) is an interesting alternative fuel because it reduces ignition time. It was concluded that an increase of EGR rate conducts to a slower combustion process, lower temperatures, and the reduction of nitrogen oxide (NOX) emissions.

Effect of EGR strategy on combustion and emission of DMDF engine for meeting China VI emission legislation

Study on EGR mode and demand were carried out to meet with the requirements of main emission limits of China VI on a diesel methanol dual fuel (DMDF) engine equipped with Hybrid exhaust gas recirculation (EGR) system coupled with back pressure valve (BPV). According to the World Harmonized Steady-State Cycle (WHSC) test cycle, the effects of EGR mode under high methanol energy ratio (MER) on the combustion, emissions and economy of DMDF engines were studied without the help of selected catalyst reduction (SCR). Considering the weight based on WHSC test cycle of full load was only 0.083, and EGR demand of full load was low, the optimal EGR strategy under different loads except full load was determined for DMDF engine. The results demonstrated that through the early injection strategy with high MER, particulate matter (PM) emissions were all at an extremely low level, far below the requirements by legislation limit of 0.01 g/kWh. With the increase of EGR rate, nitrogen oxides (NOx) emissions were significantly reduced under different loads, accompanying with one or more EGR modes at 25%, 50%, and 70% loads to ensure that NOx emission could meet the requirements by legislation limit of 0.4 g/kWh, while PM emissions were at a very low level at the same time. Demand for EGR rate of light loads was generally higher than that for medium loads, but under light loads, each of hybrid EGR modes could meet the demand of China VI legislation. While under medium loads, the dual loop (DL) EGR modes, i.e., both low pressure (LP) and high pressure (HP) EGR mode must be needed. In LP EGR mode combined with back pressure valve (BPV), higher EGR rate was required under the same NOx control target, owing to the higher intake air volume than those of other modes. The trade-off relationship in HP_BPV mode between NOx and PM emissions still existed, and high EGR rate often leaded to an increase in PM.

Combustion and emissions behaviors of a stoichiometric GDI engine with simulated EGR (CO2) at low load and different spark timings

Exhaust gas recirculation (EGR) is one of the most effective measure to control NOX emissions in the engines. CO2 was introduced to intake as simulated EGR (CO2), the combustion and emissions behaviors of a stoichiometric GDI engine with simulated EGR (CO2) at engine speed of 1500 rpm, engine load of 25% and different spark timings were studied experimentally. Experimental results show that EGR and retarded spark timing would slow the combustion. At the same EGR rate, the effect of actual EGR on combustion parameters is much greater than that of simulated EGR (CO2). A large amount of inert gas in EGR will greatly aggravate combustion, leading to increase COVimep. The order of COVimep is actual EGR rate = 15% ≫ simulated EGR (CO2) rate = 15% > EGR rate = 0%. Spark timing has little effect on BSCO and BSHC for with/without EGR at low load. At any constant spark timing, BSCO actural EGR rate = 15% ≫ BSCO simulated EGR (CO2) rate = 15%> BSCO EGR rate = 0%. BSNOX and soot emissions decrease significantly with retarding spark timing for with/without EGR. BSNOX and soot emissions show same tendencies with retarding spark timing and increasing EGR rate. BSNOX emissions is actual EGR > simulated EGR (CO2) ≈ retarded spark timing. At a constant spark timing, soot actual EGR rate = 15%< soot simulated EGR (CO2) rate = 15%< soot EGR rate = 0%. EGR reduces reaction rate of soot formation and rises the oxidation rate of soot.

Study on the Effects of EGR and Spark Timing on the Combustion, Performance, and Emissions of a Stoichiometric Natural Gas Engine.

This paper involved conducting an experimental investigation on the effects of exhaust gas recirculation (EGR) and spark timing on the combustion, performance, and emission characteristics of a China-VI heavy-duty, natural gas engine fueled with high-methane content. The results showed that increasing the EGR rate extends the spark timing range and slows the combustion. This then increases ignition delay, prolongs combustion duration, and decreases heat release rate. Peak in-cylinder pressure (PCP) and indicated thermal efficiency (ITE) initially increase because of higher boost pressure with increasing EGR rate. However, as EGR rate increases further, PCP and ITE begin to decrease because of the deviation of combustion phasing. Lower in-cylinder temperature caused by higher EGR rate may cause nitrogen oxide (NOx) emissions to reduce significantly, while total hydrocarbon (THC) and carbon monoxide (CO) emissions increase, and THC emissions could increase exponentially at high EGR rates. In-cylinder pressure, temperature, and heat release rate increase with early spark timing, but the rate of increase is reduced at higher engine speeds. Early spark timing causes THC and CO emissions to increase at part-load conditions, whereas there is little change at full-load conditions. NOx emissions also increase with early spark timing because of the higher in-cylinder temperature.

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.

Experimental study of effects of exhaust gas recirculation on combustion, performance, and emissions of DME-biodiesel fueled engine

The effects of exhaust gas recirculation (EGR) on the combustion, performance, and emissions of a six-cylinder turbocharged common-rail dimethyl ether engine with biodiesel blends were experimentally investigated. The proportions of biodiesel were 0% (B0), 5% (B5), 10% (B10), 15% (B15) and 20% (B20) by weight, and the effect of the engine load was considered. The results indicate that a higher EGR rate increases the ignition delay and combustion duration. The peak rate of heat release increases as the EGR rate increases at low loads but decreases at high loads. The present investigation shows that the EGR strategy is effective for suppressing NOx formation and the NOx emissions approximately linearly decrease as the EGR rate increases. The retardation of the combustion phase by external EGR effectively reduces the rate of pressure increase. The effect of the biodiesel proportion on the combustion and performance of an engine is complex, and the B5 blend showed the shortest ignition delay and the highest brake thermal efficiency. The influence of the biodiesel proportion on the EGR is not obvious. The disadvantages of EGR and biodiesel addition include the resultant increases in the CO and HC emissions and the particle number concentration.