High Exhaust Gas Recirculation Research Articles

The influence of injection pressure and exhaust gas recirculation on a VCR engine fueled by microalgae biodiesel

AbstractBiodiesel has been chosen as a decent alternative to diesel in the context of establishing environmentally pleasant conditions and saving petroleum‐based resources for future generations. It is well‐established that biodiesel‐powered diesel engines may achieve outcomes equivalent to those of diesel engines. The current investigation was conducted to study the effect of injection pressure (190, 210, and 230 bar) and exhaust gas recirculation (EGR) (5%, 10%, and 15%) on a single‐cylinder variable compression ratio (VCR) diesel engine running using a B20 (20% MB + 80% PD) blend of microalgae biodiesel (MABD). This experiment was conducted in two stages. During the first stage of experimentation, the efficiency and emission characteristics of a diesel engine with a B20 blend of MABD at various fuel injection pressures and fresh air were investigated. During the second phase, fresh air was mixed with 5%, 10%, and 15% exhaust gases, and the experiment was conducted. It was discovered that increasing injection pressure to 230 bar provided considerable improvements. Brake thermal efficiency increased by 2.35%, brake‐specific fuel consumption decreased by 3.57% and pollutants such as carbon monoxide (CO), hydrocarbon, and smoke were reduced by more than 50% compared to conventional diesel. These reductions were similarly significant (over 22%) as compared to the B20 blend at lower injection pressure (210 bar). However, there was a slight trade‐off: nitrogen oxide (NOx) emissions increased partially (3.14%), while exhaust gas temperature (EGT) increased by 1.72% at a higher pressure. The study then investigated the influence of EGR (5%, 10%, and 15%) at various injection pressures. The optimal value seems to be 10% EGR at 230 bar injection pressure. This combination substantially reduced NOx emissions (by over 41% compared to the normal B20 blend) and EGT (by more than 8%), while having no notable effect on other performance or emission variables. Overall, the results show that employing a B20 MABD blend with high injection pressure (230 bar) and moderate EGR (10%) improves engine performance while reducing hazardous emissions.

Impact of Cylinder-to-Cylinder Dispersion of Exhaust Gas Recirculation on the Three-Way Catalyst Performance and Tailpipe Emissions of Spark-Ignition Engines

Abstract New generations of spark-ignition engines include exhaust gas recirculation (EGR) to improve the engine efficiency. Depending on the design of the EGR routing, some differences in the total amount of recirculated gases that reach each cylinder can be induced. This affects the air-to-fuel ratio on each cylinder due to the combination of the different temperature and composition of the gases at the intake valve closure. As a consequence, significant deviations in the combustion process and the subsequent composition upstream the three-way catalyst can be reached. This paper explores these effects on catalyst performance and tailpipe emissions, individualizing the behavior for each regulated species. The study was performed in a four-cylinder naturally aspirated engine with Atkinson cycle and a close-coupled three-way catalyst. The most significant deterioration in conversion efficiency appeared for the nitrogen oxides, directly linked to the EGR dispersion level. In the case of carbon monoxide (CO) emissions, no significant impact was observed except at high average EGR rates, where one or more of the cylinders exceeded the EGR tolerance for that speed and load. Based on these results, a strategy where the fuel injector command is adapted to correct the air-to-fuel ratio deviations induced by the EGR was developed and implemented.

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

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

Matching and optimization to minimize fuel consumption and NOx emission for a marine diesel engine with turbo-assisted exhaust gas recirculation

Exhaust gas recirculation (EGR) and two-stage turbocharging technology are widely used in marine diesel engines due to their advantages of reducing nitrogen oxides (NOx) emission and improving fuel economy respectively. The matching of EGR, two-stage turbocharging and diesel engine is significant to realize both advantages simultaneously. Turbo-assisted EGR (TA EGR) can achieve high EGR rate and lower fuel consumption due to a turbocharger driving EGR. In this study, a 1D model of the diesel engine with TA EGR coupling two-stage turbocharging system was established by GT-Power. A theoretical matching method was proposed based on the requirements of excess air coefficient and EGR rate. The matching laws of the coupling system were studied, and the preliminary matching results achieved good effects. A fully connected neural network was used as the optimization agent model of the 1D model, and the NSGA II algorithm was used to carry out the multi-parameter and multi-objective optimizing matching. Considering constrained and unconstrained conditions, independent optimizing matching was carried out under each single load, and the weighted brake specific fuel consumption (BSFC) and weighted NOx under all loads were taken as the target to carry out comprehensive optimizing matching. The results showed that the optimization performance is worse under constrained conditions, while TA EGR coupling adjustable two-stage turbocharging system can achieve comprehensive optimal BSFC and NOx, with weighted BSFC decreasing by 3.57% and weighted NOx decreasing by 75.28% compared with experimental results of the original engine.

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.

Effects of asynchronous late intake valve closing combined with high geometric compression ratio and exhaust gas recirculation on combustion and fuel consumption in a turbocharged SI engine:An experimental study

To achieve low-carbon transportation, a novel Miller cycle was implemented by using asynchronous late intake valve closing (ALIVC) in the high compression ratio turbocharged SI engine. The effects of the Miller cycle on combustion and performance were investigated and compared with the original Otto cycle. Based on this, EGR was introduced and its effects on Miller cycle engine performance and energy balance were investigated. The results show that the Miller-CR12.5 can reduce pumping loss and suppress knock without sacrificing power output. Compared to the Otto-CR10.5, the Miller-CR12.5 achieves a 6.7 % reduction in BSFC at the lowest fuel consumption point and a 10–11.4 % reduction at high loads. The lower peak combustion temperature allows the Miller-CR12.5 to eliminate fuel-enriched injection at high loads, reducing the heat transfer and combustion loss. The introduction of EGR in the ALIVC Miller cycle engine decreases the peak HRR and extends the combustion duration. However, the advanced 50 % combustion position and increased effective expansion ratio can improve engine performance. At 10 % EGR rate, the BSFC obtains a 2.1 % reduction and NOx emissions are reduced by 62 %. As the EGR rate increases, the heat transfer and exhaust loss decrease, but there is a slight increase in combustion loss.

Study on Control Strategies on NOX Emissions to Meet Real Driving Emissions.

The aim of this study was to fulfill the NOx emissions standards for a light-duty diesel vehicle under real driving emissions (RDE) testing conditions by implementing various control strategies. In this study, RDE tests were performed by adjusting the air mass quantity and postinjection quantity in order to analyze engine-out and tail-pipe nitrogen oxides (NOx) emissions for different phases of RDE. The results showed that reducing in air mass quantity enabled the engine to operate in higher exhaust gas recirculation (EGR) rate regions, resulting in a 32.5% reduction in engine-out NOx emissions and an 80.4% decrease in tail-pipe NOx emissions. Increasing the postinjection quantity primarily enhanced the NOx conversion efficiency for the urban phase by 7.5%, leading to a 22.6% reduction in tail-pipe NOx emissions. By employing both strategies, vehicles can comfortably meet the CN6b emission regulations by a substantial margin.

Efficiency of limiting nitrogen oxides emissions by exhaust gas recirculation systems of marine internal combustion engines

The subject of this study is systems for ensuring environmental safety of marine internal combustion engines, in particular, technologies for limiting emissions of nitrogen oxides (NOx). The regulatory requirements for reducing emissions are presented in the paper. The main theoretical aspects of the problem of nitrogen oxides formation during combustion in a diesel engine are considered. On the basis of these theoretical aspects the effectiveness of using various methods to achieve the requirements for the permissible level of NOx concentration in the exhaust gases is assessed. Exhaust gas recirculation (EGR) systems and selective catalytic reduction (SCR) systems are considered as the main technologies; they allow achieving the highest indicators of nitrogen oxide emissions control in accordance with the requirements of the Tier 3 standard. Taking into account the peculiarities of the requirements for the design and layout of systems as part of a ship power plant, as well as operational and investment costs, the main attention in the work is paid to systems of indirect influence on the engine in-cylinder processes, which include exhaust gas recirculation systems. Based on the comparison of high and low pressure EGR, the advantages and disadvantages of the designs are determined. It is noted that high-pressure exhaust gas recirculation systems have a number of advantages, which primarily include the compactness and high speed of the system response to changes in operational conditions. On the example of the leading manufacturers developments, the potential capabilities of the high-pressure EGR system and the engine characteristics confirming the effectiveness of its use are demonstrated. Based on the results of the work, a conclusion about the high efficiency and expediency of using exhaust gas recirculation systems to meet the requirements of the current environmental safety standards of ship power plants is made.

Comparative analysis of thermal and non-thermal discharge modes on ultra-lean mixtures in an optically accessible engine equipped with a corona ignition system

Radio-Frequency corona-based ignition systems are currently being investigated by the engine research community for their capability to ensure robust combustion at challenging operating conditions such as lean mixture and/or high exhaust gas recirculation (EGR) dilution. The low-temperature plasma (LTP) produced by the corona discharge accelerates the early flame development thanks to the production of combustion precursors like radical and excited species. Plasma benefits can be maintained with extensive management of the control parameters, preventing the transition from the non-thermal discharge mode to a thermal one.However, under ultra-lean conditions, where the ignition probability significantly decreases, the LTP discharge may not be suitable for promoting the combustion process because of insufficient thermal energy transfer and scarcity of available fuel, which is essential for radical production. Therefore, it may be necessary to increase the volume in which the plasma interacts to ensure robust ignitions and stable flame propagations. For this reason, the present work aims to assess and quantify the differences, in terms of combustion performance, between a corona igniter operating at LTP mode and with electric arcs occurring, at ultra-lean operating conditions. In arc-mode, the igniter produces volumetric discharges, facilitating extensive mixing of the mixture and resulting in advantageous effects on kernel formation and propagation. Tests were carried out in a single-cylinder optical access engine under low load and low speed, using gasoline as fuel. Close to the leanest stable limit found, the LTP mode shows a lower cycle-to-cycle variability. Above such a threshold, the thermal discharge can guarantee stable combustion events while the LTP discharge leads to unstable working conditions. Indicating, imaging, and pollutant emission analysis are carried out to evaluate the effects of thermal and non-thermal plasma modes on combustion characteristics and their environmental impact.

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.

Tyre pyrolytic oil blends in a state-of-the-art compression ignition engine: Towards fuel-optimised combustion

The end-to-end efficiency and environmental impact of tyre pyrolysis oil (TPO) are currently high on the agenda of worldwide research. However, most knowledge regarding combustion and emissions of TPO fuels comes from legacy (pre-Euro standard) engine platforms, operating in non-optimal combustion conditions. The few tests on modern automotive engines have used factory, diesel-optimised calibration maps and focus on only small TPO admixtures to diesel fuel (DF). The present work aspires to tackle these knowledge gaps by testing higher TPO admixture diesel blends in a state-of-the-art research engine realising low nitrogen oxides (NOX), partially premixed compression ignition. Measurement campaigns focus on accuracy in establishing fuel-to-fuel differences in emissions, also with consideration of unlegislated species. A combination of thorough combustion analysis and accurate fuel property characterisation allows evaluation of a calibration strategy that harnesses multi-pulse injection and a fully controlled air-path to mitigate emissions. This strategy enables an engine fuelled with a 40% TPO blend to realise low-temperature combustion in a wider area of the calibration map than is possible with DF. The most favourable NOX/particulate matter (PM) mode is extended towards high exhaust gas recirculation and early injection regimes. Adopting this dedicated engine control for TPO allows best-point NOX/PM emissions of 1.22 g/kWh and 0.18 g/kWh respectively, while maintaining the baseline indicated thermal efficiency target of 42%. Carbon monoxide and hydrocarbons emissions are elevated, but in terms of current EU Non-road Mobile Machinery Stage V limits, differences between TPO and DF are insignificant. However, regardless of calibration, TPO's chemical make-up causes increased emissions of sulphur oxides and aromatic hydrocarbons.

Numerical investigations on the effects of EGR routes on the combustion characteristics and efficiency of a heavy-duty SI methanol engine

Exhaust gas recirculation (EGR) is one effective strategy to improve the thermal efficiency of the heavy-duty spark-ignition (SI) methanol engine. The high EGR tolerance of methanol engine raises new requirements for the EGR system. In this study, the influences of three different EGR routes, high-pressure EGR (HP-EGR), low-pressure EGR (LP-EGR), and high-low-pressure EGR (HLP-EGR) on the engine performance were studied by the one-dimensional simulation with the predictive combustion sub-model. The investigation was conducted at 1000 rpm and 1400 rpm, and 50% and 100% full load. Results show that EGR routes influence both the combustion characteristics and pumping mean effective pressure (PMEP), thus affecting the brake specific fuel consumption (BSFC). The EGR route with the lower internal EGR rate has a lower in-cylinder temperature at the compression stroke, a weaker knock tendency and a more advanced combustion phase. The effects of EGR routes on BSFC are more significant at the higher engine speed. The optimal BSFC of HP-EGR is lower than that of HLP-EGR and LP-EGR by up to 16.4 g/k·Wh and 21.2 g/k·Wh. Considering the engine performance at all engine operating conditions, HP-EGR is the optimal EGR route while LP-EGR is the worst one for the heavy-duty SI methanol engine.

Reducing Soot Nanoparticles and NOX Emissions in CRDI Diesel Engine by Incorporating TiO2 Nano-Additives into Biodiesel Blends and Using High Rate of EGR

The developments in the field of nano-additives have increased in the recent years due to the desire to reduce the level of exhaust emissions in diesel engines. The soot characteristics of particulate matter (PM) and nitrogen oxides (NOX) were experimentally investigated using two concentrations of titanium dioxide (TiO2) as nano-additives (25 ppm and 40 ppm) blended with C20D (composed of 20% castor oil methyl ester and 80% diesel fuel) and 30% exhaust gas recirculation (EGR). The combustion of C20D + TiO2 increases brake thermal efficiency (BTE) by 2.8% in comparison with neat C20D, while a significant reduction was obtained in BSFC 6.5% and NOX emissions were maintained at a level parallel with diesel. The results indicated that the technique involving a high EGR rate and the addition of 25 ppm and 40 ppm of TiO2 nanoparticles to the C20D exhibits better reductions in NOX emissions by 17.34% and 21.83%, respectively, compared to the technique comprising the use of C20D + TiO2 and C20D. The reduction in the total concentration of PM via the addition of TiO2 nanoparticles to the C20D was 26.74% greater than neat C20D and diesel. In contrast, the incorporation of a high rate of EGR with C20D +TiO2 increased the PM concentrations by 16.85% compared to the technique without EGR. Furthermore, the high concentrations of TiO2 nanoparticles (40 ppm) in the C20D produced 19 nm smaller soot nanoparticles compared to the 23 nm larger soot nanoparticles produced from the low concentrations of TiO2 nanoparticles (25 ppm) added into the C20D. The current investigation reveals that the reduction in NOX emissions and the production of soot nanoparticles notably improved due to the synergic effect of EGR, the TiO2 nanoparticles, and biodiesel.

Effect of High and Low Pressure EGR on Diesel Engine Matched with Mechanical Turbo-compound

The mode of exhaust gas recirculation (EGR) and the flow of recirculated exhaust greatly impact the exhaust heat recovery of the mechanical turbo-compound. A matching mechanical turbo-compound of the diesel engine is established with GT-power software to study the effect of EGR mode and EGR rate on it, and the effect of EGR rate on the working performance of diesel engine and the mechanical turbo-compound under high-pressure EGR mode and low-pressure EGR mode is also studied. The results show that compared with the original engine, the effective thermal efficiency of the diesel engine matched with mechanical turbo-compound has been improved. Under the two EGR modes, as the EGR rate increase, the effective thermal efficiencies of diesel engine matched with mechanical turbo-compound and the original engine are decreasing. Under the maximum torque condition, the fuel economy of mechanical compound turbine diesel engine matched with low-pressure EGR system is better than with high-pressure EGR system; while underrated power condition, the fuel economy difference of mechanical compound turbine diesel engine matched with high-pressure EGR system and low-pressure EGR system is small.

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

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

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

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

Experimental Study and Optimisation of a Non-Conventional Ignition System for Reciprocating Engines Operation with Hydrogen–Methane Blends, Syngas, and Biogas

The paper deals with the experimental study of a medium-load spark ignition engine under operation with different fuel mixtures among those deemed as promising for the transition towards carbon-free energy systems. In particular, the performance of a non-conventional ignition system, which permits the variation of the ignition energy, the spark intensity and duration, was studied fuelling the engine with 60–40% hydrogen–methane blends, three real syngas mixtures and one biogas. The paper is aimed to find the optimal ignition timing for minimum specific fuel consumption and the best setup of the ignition system for each of the fuel mixtures considered. To this end, a series of steady-state tests were performed at the dynamometer by varying the parameters of the ignition system and running the engine with surrogate hydrogen–methane–nitrogen mixtures that permit the simulation of hydrogen–methane blends, real syngas, and biogas. The results quantify the increase of spark advance associated with the decrease of the fuel quality and discuss the risk of knock onset during methane–hydrogen operation. It was demonstrated that the change of the ignition system parameters does not affect the value of optimum spark advance and, except for the ignition duration, all the parameters’ values are generally not very relevant at full load operation. In contrast, at partial load operation with low-quality syngas or high exhaust gas recirculation rate, it was found that an increase of the maximum ignition energy (to 300 mJ) allows for operation down to approximately 66% of the maximum load before combustion becomes incomplete. Further reductions, down to 25% of the maximum load, can be achieved by increasing the gap between the spark plug electrodes (from 0.25 to 0.5 mm).

Experimental investigation on emission characteristics of high reactivity gasoline compression ignition with different EGR and injection pressure strategies

Using a High Reactivity Gasoline (HRG) in diesel engines is a promising approach to reduce NOx and soot emissions simultaneously without modifying the engine hardware. In this study, an experimental investigation on HRG and diesel emission characteristics was conducted in a six-cylinder heavy duty diesel engine with different exhaust gas recirculation (EGR) rate and injection pressure strategies. Four operation points, A25, A75, C25, and C75 in the European Steady Cycle (ESC), were studied. The pilot-main injection strategy was applied, and injection timing was adjusted to maintain a constant Crank Angle of 50 % heat release (CA50). The results show that, compared with diesel, HRG can achieve lower soot mass emission while maintaining an ultra-low NOx emission level (2–3 g/kWh) with a lower injection pressure, indicating lower cost in the fuel injection and aftertreatment systems. The particle size distribution was also analyzed for both fuels. Under high EGR rates, the accumulation mode particles were dominant for both HRG and diesel. However, under low EGR rates, diesel produced much more nucleation mode particles than HRG. The phenomenon can be explained by the difference in the pyrene and acetylene productions between paraffin and aromatic compositions.

Assessment of air management strategies to improve the transient response of advanced gasoline engines operating under high EGR conditions

Advanced gasoline engines may lead the medium-term future of the passenger vehicle market, working in conventional and hybrid powertrains. Downsizing with turbocharging is the most extended way to improve fuel economy in gasoline engines. It is also proven that exhaust gas recirculation (EGR) reduces fuel consumption, but extracting the maximum benefit from EGR requires operating with high EGR rates. This fact can compromise the transient engine operation due to the greater turbocharger dependence. This research evaluates the EGR influence on the transient response of a turbocharged gasoline engine and, mainly, the potential of three air management strategies to accelerate the said response. Tip-in maneuvers at 1500 rpm (6–12 bar BMEP) were tested and simulated to this end. The three strategies are: reducing the EGR dilution by closing the EGR valve simultaneously with the throttle opening, using a pressurized air tank (PAT), and installing an electric supercharger at the compressor outlet in series. Engine tests show that the torque response time with EGR is 2-s slower than without EGR. 1D modeling results reveal that: the PAT connected to the intake manifold provides the fastest response, and the electric supercharger guarantees an excellent tradeoff between fuel consumption and torque response.

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.