EGR Gas Research Articles

Numerical studies on the flow characteristic of the marine two-stroke engine integrated with the high-pressure exhaust gas recirculation system

The high-pressure exhaust gas recirculation (HP-EGR) has been well-proven for marine engines complying with the IMO Tier Ⅲ NOx regulation. Considering different turbocharged scavenging schemes and emission control modes, intake and exhaust gas management is critical to the HP-EGR design. However, few theoretical studies on it were reported. This paper aims at providing a case study on the flow characteristic of the turbocharged HP-EGR system. With the proposed topology structure of the typical HP-EGR layout, numerical studies on the turbocharged scavenging and EGR design were conducted based on the 6EX340 two-stroke engine. The result showed that the flow characteristic of the turbocharged two-stroke engine can be graphically depicted by simplifying the cylinder and turbine as multi-nozzle in series. According to the nozzle flow equation of uniflow scavenging, there exists an optimum turbine flow area to maximize the scavenging mass flow. Effects of EGR, cylinder bypass, and exhaust gas bypass on the flow characteristic of the two-stroke engine depend on the turbocharger matching. The out-cylinder scavenging and in-cylinder combustion should be optimized interactively to fully explore the fuel economy and NOx trade-off. Finally, the proposed design procedure can provide good guidance for the design and control of the HP-EGR system.

Elucidating NO coupling effects on ignition of toluene reference fuels by chemical functional group analysis

Derived cetane number (DCN), Research and Motor Octane Numbers (RON and MON) have been fundamentally analyzed using Quantitative Structure-Property Relationship (QSPR) regression models with key chemical functional groups. Both RON and MON exhibit strong sensitivities to the abundances of (CH2)n and benzyl-type groups but lack sensitivity to the CH3 group, most dominant in real gasolines. Residual and EGR gases contain NOx known to synergize with fuel autoignition chemistry. Two TRF mixtures having high and low aromatic content but sharing the same RON and MON values were used to evaluate NOx coupling effects. DCN measurements with NO addition were found to be strongly correlated with the abundance of the (CH2)n group. Similar experiments of 200 ppm NO in a Rapid Compression Machine show promotion (inhibition) of ignition for the high (low) aromatic TRF fuel. Kinetic modeling attributes the promotion to the NONO2 interconversion reactions, NO + HO2 = NO2 + OH, CH3 + NO2 = CH3O + NO and NO2 + H = NO + OH. The inhibitive effect relates specifically to low temperature kinetics and high NO loading conditions, leading to the formation of meta-stable species (e.g. CH3 + NO2 (+M) = CH3NO2 (+M)) that decelerate the rate of conversion of HO2 to more reactive OH radicals. The coupling of NO with real gasolines depends on chemical composition and temperature conditions not only encompassed by RON and MON criteria, but by the chemical functional group characteristics. The relevance of this finding to the significance of preferential vaporization of multi-component gasolines on low-speed pre-ignition (LSPI) is discussed. Within the context of chemical functional group distributions of five distillation cuts of a marketed ethanol-free gasoline determined by NMR spectroscopy, the analyses identify considerable variations of key functionalities with fuel distillation properties, indicating chemical kinetic autoignition behaviors that are dependent on preferential vaporization.

Influences of inner surface of pipe on deposit formation

Engine deposits in exhaust gas passages cause the increase of the pumping loss and the failing of the valve action. Deposits also affect EGR gas temperature in cooled EGR system because their thermal conductivity is low. Therefore, it is necessary to reduce engine deposits in order to improve engine performance. In this study, the influences of the inner surfaces of pipe on deposit formation are investigated by comparing the deposition on SUS304 and two kinds of fluorocarbon polymer, PTFE(polytetrafluoroethylene) and PFA(copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether). Deposits are experimentally formed by smoke produced when diesel fuel is burning in an alcohol lamp or actual exhaust gas emitted from a gasoline engine. The results indicate that different surfaces make difference to the amount and shape of deposits. In addition, it is suggested that small Van der waals force and non-wettability contribute to deposit reduction.

Reforming of toluene with simulated automobile exhaust gas over hydrotalcite-like-compound-derived Ni catalyst

Reforming of toluene, which is a model compound of gasoline, with model exhaust gas (model EGR gas) of gasoline engine was carried out with Ni catalyst. The Ni/Mg/Al catalyst prepared from hydrotalcite-like precursor compound showed higher performance than Ni/α-Al2O3 catalyst in terms of activity, stability and coke deposition resistance. The activity of Ni/Mg/Al after the initial deactivation was about 1/200 of Rh/CeO2 based on the weight of active metal (Ni or Rh), and the difference was much smaller than that of price between Ni and Rh. The amount of coke deposition on Ni/Mg/Al catalyst was increased with increases of W/F or partial pressure of toluene, especially at the outlet of the catalyst bed, where the coke formation is mainly due to CO disproportionation. The deactivation was also severer in larger partial pressure of toluene when the toluene feed was changed while partial pressure of H2O, N2 and CO2 was set constant to the model EGR gas. Large steady state H2 formation and high conversion were obtained at conditions with low partial pressure of toluene, similarly to the case of simple steam reforming, the Ni/Mg/Al catalyst after reaction can be regenerated by the combination of oxidation (at 773 K) and reduction (at 1073 K) treatments. The effect of feed ratio of H2O:N2:CO2 showed that low partial pressure of steam in model EGR gas in comparison with standard feed gas for steam reforming is the main reason for low toluene conversion and coke deposition resistance. On the other hand, the presence of CO2 did not affect the conversion and the coke deposition behavior so significantly.

EGR gas composition effects on ignition delays in diesel combustion

This paper presents the effects on ignition delays of a range of exhaust gas compositions recirculated in the intake air. The ignition delays were measured in a single-cylinder diesel engine introducing a variety of hydrocarbons, nitrogen oxides (NOx), and carbon monoxide (CO) into the intake gas, and changing the concentrations of these components. The experimental results show that the ignition delay decreases with the NOx addition, NO2 promotes the ignition more than NO, and this effect is more pronounced at higher intake gas temperatures. The ignition delay decreases with HC addition under NOx rich conditions while there is little effect under low NOx conditions, and the ignition delay changes with the kinds of hydrocarbons. The CO has little effect on the ignition delay. With the aid of chemical reaction analysis, the mechanisms of these changes are elucidated.

Impact of Electrically Assisted Turbocharger on the Intake Oxygen Concentration and Its Disturbance Rejection Control for a Heavy-duty Diesel Engine

The electrically assisted turbocharger (EAT) shows promise in simultaneously improving the boost response and reducing the fuel consumption of engines with assist. In this paper, experimental results show that 7.8% fuel economy (FE) benefit and 52.1% improvement in transient boost response can be achieved with EAT assist. EAT also drives the need for a new feedback variable for the air system control, instead of the exhaust recirculation gas (EGR) rate that is widely used in conventional turbocharged engines (nominal system). Steady-state results show that EAT assist allows wider turbine vane open and reduces pre-turbine pressure, which in turn elevates the engine volumetric efficiency hence the engine air flow rate at fixed boost pressure. Increased engine air flow rate, together with the reduced fuel amount necessary to meet the torque demand with assist, leads to the increase of the oxygen concentration in the exhaust gas (EGR gas dilution). Additionally, transient results demonstrate that the enhanced air supply from the compressor and the diluted EGR gas result in a spike in the oxygen concentration in the intake manifold (Xoim) during tip-in, even though there is no spike in the EGR rate response profile. Consequently, there is Nitrogen Oxides (NOx) emission spike, although the response of boost pressure and EGR rate is smooth (no spike is seen). Therefore, in contrast to EGR rate, Xoim is found to be a better choice for the feedback variable. Additionally, a disturbance observer-based Xoim controller is developed to attenuate the disturbances from the turbine vane position variation. Simulation results on a high-fidelity GT-SUTIE model show over 43% improvement in disturbance rejection capability in terms of recovery time, relative to the conventional proportional-integral-differential (PID) controller. This Xoim-based disturbance rejection control solution is beneficial in the practical application of the EAT system.

Experimental investigation on methanol auto-ignition in a compression ignition engine under DMDF mode

At high loads, Diesel-Methanol Dual Fuel (DMDF) engines strongly rely on high methanol substitution for diesel proportion (MSP) to achieve high efficiency combustion and reduce nitrogen oxides (NOx) and soot emissions. However, high MSP is limited by the probability of methanol auto-ignition. The experimental study was conducted to investigate into the influence factors of methanol auto-ignition under diesel engine conditions at 50% of full load. Meanwhile the testing results concerning combustion characteristics and emissions have been analyzed. Experimental results showed that if there was apparent heat release before TDC, which was earlier than diesel fuel injection, it indicated that methanol auto-ignition occurred. In order to avoid methanol auto-ignition which is very easily to cause knock or rapid pressure rise, the in-cylinder mean temperature should be less than 990 K (at this case, the intake temperature was 338 K) before diesel injection timing. As intake temperature increased, methanol heat release timing was advanced and the heat release rate (HRR) was gradually accelerated. If the injection timing of diesel was later than that of methanol auto-ignition, almost all diesel fuel would be burned in the form of diffusion combustion in the methanol flame, leading to the increase of soot emissions. Methanol auto-ignition would be inhibited by EGR gas. The EGR and MSP had a great impact on both the ignition timing and the peak HRR of methanol auto-ignition. As EGR ratio increased, so did the incomplete combustion loss of methanol. As long as methanol auto-ignition occurred, the increase of MSP would result in a decrease in NOx emissions, but soot emissions were increased instead.

Alkanes based two-stage expansion with interheating Organic Rankine cycle for multi-waste heat recovery of truck diesel engine

The environment issue combined with the rising of crude oil price has attracted more attention in waste heat recovery of diesel engine. The Organic Rankine cycle (ORC) offers a good solution to utilize multi-grade waste heats of diesel engine. Conventional multi-source ORC systems are too complex for vehicle application. This paper proposed a two-stage expansion with interheating organic Rankine cycle (ORC) system using alkanes as working fluids, in order to recover multi-waste heats (exhaust gas, EGR gas and engine coolant) with simple system configuration and solve the problem of overlarge expansion ratio of alkanes. Thermodynamic models based on first and second thermodynamic law are established. A correlation was proposed to estimate the optimum intermediate pressure to achieve maximum net power output. System performance comparison among alkanes shows that cyclic alkanes are superior to linear alkanes regarding net power output, thermal efficiency and exergy losses although they are weaker in recovering heat from engine coolant. Compared with the conventional preheating-regenerative ORC system, the proposed system can recover waste heat of exhaust gas (100%) and EGR gas (71.8%) more efficiently and generate 6.7% more output power, and it is more compact in terms of heat exchangers size, pump volumes and turbine structure.

Calorimetry and Imaging of Plasma Produced by a Pulsed Nanosecond Discharge Igniter in EGR Gases at Engine-Relevant Densities

Calorimetry and Imaging of Plasma Produced by a Pulsed Nanosecond Discharge Igniter in EGR Gases at Engine-Relevant Densities

Measurement of Laminar Burning Velocity of Combustible Mixtures Containing Simulated EGR Gas

Measurement of Laminar Burning Velocity of Combustible Mixtures Containing Simulated EGR Gas

SECFR 시스템의 차량적용을 위한 분무균일도향상에 관한 연구

Abstract Lower recirculated gas temperature at EGR system reduces NOx and PM emissions. However, EGR Cooler can bepolluted by PM generated from recirculated EGR gas, and it reduces cooling efficiency and the amount of EGR gassimultaneously. The SECFR(Steam EGR Cooler Fouling Remover) system which uses the evaporated washer fluidsteam caused by high temperature of EGR gas was manufactured for removing fouling generated on the cooler surface.Since an injection pressure of wind shield washer fluid in the vehicle is approximately 0.5 bar, it is not enough toatomize the injected washer fluid. Thus, it is necessary to apply a method to atomize the washer fluid. In this study,the impinging plate was used to promote the atomization of spray washer fluid for the purpose of apply SECFR sys-tem to vehicles and measured the DAR(Droplet Area Ratio) and DUI(Droplet Uniformity Index) through the sprayvisualization. 기호설명 EGR : 배기가스재순환NOx : 질소산화물PM : 입자상 물질HC : 미연 탄화수소CO : 일산화탄소DUI : 액적균일도DAR: 액적분포면적율

Application of a multi-zone combustion model to investigate the NOx reduction potential of two-stroke marine diesel engines using EGR

The most promising solution for propulsion of marine vessels currently and for the near future is the two-stroke low-speed diesel engines. Despite its advantages, as far as specific fuel oil consumption, power density and reliability is concerned, it suffers from increased NOx emissions mainly because of its low rotational speed. But the upcoming NOx emission legislation (Tier III) in the marine sector requires considerable reduction of NOx emissions towards levels which have not yet been commercially achieved using primary methods. This creates new challenges for the development and application of innovative techniques that could reduce engine’s NOx emissions with the lowest possible fuel penalty. This is important considering current and future fuel prices. The large size of the 2-stroke marine engine makes the use of experimental techniques, to investigate this potential, expensive and time consuming. Modelling can significantly contribute towards this effort and result to reduction of research and development cost. Among the most effective in-cylinder techniques for NOx reduction is EGR, a proven technology for smaller engines used in the transport sector. In the present study, it is investigated via modelling, the potential to reduce NOx emissions of two-stroke marine engines using EGR. Despite the technological difficulties resulting mainly from the use of Heavy Fuel Oil (HFO), which makes the application of conventional EGR techniques difficult, it is worthwhile investigating the NOx reduction potential, since significant progress has been achieved towards the development of new EGR gas cooling techniques and scrubber technologies for removal of sulphur species from the exhaust gas. The present investigation makes use of an existing well validated multi-zone combustion model, initially developed for high-speed DI diesel engines. The model has been successfully applied in the past, to investigate heavy duty diesel engine NOx reduction via EGR, providing favourable results. Currently it is modified and applied on a two-stroke marine diesel engine using EGR. Model evaluation is based on experimental data acquired from the international literature, due to lack of experimental data for 2-stroke engines. The analysis of derived results reveals model’s ability to predict both engine performance and NOx emissions but most important the ability to predict the overall effect of EGR on NOx emissions in a qualitatively correct way. The results also reveal the strong potential of EGR to control NOx emissions of 2-stroke engines with relatively low fuel penalty compared to alternative techniques.

F141 CO_2添加プロパン予混合微小層流火炎の燃焼速度特性に関する実験的研究(OS-03:革新的技術のための燃焼研究(2))

This study is performed to examine experimentally the effects of CO_2 as one of EGR gas on the burning velocity of the propane-oxygen-dilution gas premixed meso-scale spherical laminar flames with the flame radius r_f < about 5mm. The mixtures have nearly the same laminar burning velocity (S_<L0>=25cm/s) with different equivalence ratios (φ=0.5-1.4). N_2 is also examined for comparison. The radius and the burning velocity of meso-scale flames are obtained by using sequential schlieren images recorded under appropriate ignition conditions. It was clear that the burning velocity for the mixture diluted with CO_2 at the same r_f and Karlovitz number has tendency to be larger than that with N_2, except for φ=1.4.

Experimental study on the effects of high/low pressure EGR proportion in a passenger car diesel engine

An experimental study was conducted to investigate the effects of the proportion between high pressure and low pressure exhaust gas recirculation (HP/LP EGR) on engine operation. The study focused on the characteristics of combustion, emissions, and fuel consumption in a 2.2L passenger car diesel engine. The experiments were performed under three part-load and steady-state operating conditions. The LP EGR portion was swept from 0 to 1, while the mass flow rate of fresh air and boost pressure were fixed. The results showed that the intake manifold temperature decreased gradually as the LP EGR portion increased due to its greater cooling capability by a longer supply line and an intercooler. However, the required cooling power for the intercooler increased because the LP EGR gas, which has a higher temperature than the fresh air, was induced upstream of the compressor. The lowered intake manifold temperature with the increase of the LP EGR portion led to the prolonged ignition delay of pilot injections, which resulted in a slightly higher peak heat release rate in the main combustion. A higher LP EGR portion showed a lower fuel consumption level than the HP EGR only case because the variable geometry turbocharger (VGT) nozzle opened more widely to maintain the boost pressure, which means a lower pumping loss. Nitrogen oxide (NOx) emissions were also decreased as the LP EGR portion increased due to lowered intake charge temperature. Consequently, it was possible to improve the trade-off relationship between NOx emissions and fuel consumption with the increase of the LP EGR portion under steady-state operating conditions.

G0710104 予混合気の不均質性を考慮したHCCI燃焼簡易モデル([G071-01]エンジンシステム部門一般セッション(1):「HCCIエンジン」)

To predict ignition timing and combustion duration of HCCI combustion, it is necessary to consider inhomogeneity of pre-mixture such as O_2, Fuel, and temperature. Usually, CFD (Computational Fluid Dynamics) is applied to predict the inhomogeneity. However, the calculation load of CFD is heavy to use as the on-board model. In this study, a simple prediction model for ignition timing and combustion duration of HCCI combustion is developed, which can consider inhomogeneity of pre-mixture. PDF of EGR gas is employed to express the influences of inhomogeneity of O_2 and temperature in pre-mixture. This model is confirmed by comparing with the experiment result of the HCCI test bench. As a result, the predictability of this model achieves around 50% for plus minus 1.5 deg. of ignition timing and combustion duration.

Optical infrared-sensor inside the cylinder to determine the EGR- and residual gas rate in diesel engine

To meet the increased demands of new exhaust and CO2 limits a research project of Volkswagen R&amp;D, the Techni- cal University of Poznan and the Ostfalia University of Applied Sciences has been initiated; its main target was the development and adaptation ICOS (Internal Combustion Optical Sensor) - an infraredsensor of LaVision for on-line measurements of EGR-rate in cylinder of an engine under operation. The objective of the project was to determine by different optical signals the CO2 concentration, the EGR rate and residual gas which are cycle-resolved in the cylinder. In this paper the principle of measurement of optical indication has been described. The infrared sensor was validated by a one-cylinder diesel engine and compared to a synchronously running fast gas sampling system (CSV). Finally the practical application of various parameter variations is illustrated in the determination of the EGR and residual gas rate. Thus a new measurement techniąue for the development offuture generations of engines introduced.

압축착화 엔진에서 분사압이 저온연소에 미치는 영향

Diesel low temperature combustion (LTC) is the concept where fuel is burned at a low temperature oxidation regime so that <TEX>$NO_x$</TEX> and particulate matters (PM) can simultaneously be reduced. There are two ways to realize low temperature combustion in compression ignition engines. One is to supply a large amount of EGR gas combined with advanced fuel injection timing. The other is to use a moderate level of EGR with fuel injection at near TDC which is generally called Modulated kinetics (MK) method. In this study, the effects of fuel injection pressure on performance and emissions of a single cylinder engine were evaluated using the latter approach. The engine test results show that MK operations were successfully achieved over a range of with 950 to 1050 bar in injection pressure with 16% <TEX>$O_2$</TEX> concentration, and <TEX>$NO_x$</TEX> and PM were significantly suppressed at the same time. In addition, with an increase in fuel injection pressure, the levels of smoke, THC and CO were decreased while <TEX>$NO_x$</TEX> emissions were increased. Moreover, as fuel injection timing retarded to TDC, more THC and CO emissions were generated, but smoke and <TEX>$NO_x$</TEX> were decreased.

Flame front characteristics of turbulent premixed flames diluted with CO2 and H2O at high pressure and high temperature

Flame front structure characteristics of turbulent premixed flames including the local radius of curvature, fractal inner cutoff scale and local flame angle were calculated from the experimental OH-PLIF images of CH4/air flames and those diluted with CO2 and superheated H2O at 0.5MPa and 573K. The convex and concave structures of the flame front were detected and statistical analysis including PDF and ADF of the local radius of curvature and the local flame angle was conducted. Results showed that the flame front of turbulent premixed flames at high pressure and high temperature is a wrinkled flame front with small scale convex and concave cusps superimposed on large scale branches, while the whole flame front tends to be convex to the unburned mixture. The effect of EGR gas dilution on the flame front structure of turbulent premixed flames is dominated by CO2 rather than H2O dilution. The quantitative flame front characteristics reveal the complicated effect of CO2 dilution on turbulent premixed flames characteristics observed in our previous research. In the case of CO2 dilution, some local wrinkled structures become sharp and propagate deep into the burned mixture, resulting in a decrease of the fractal inner cutoff scale, the formation of a thick flame brush and the enlargement of the mean flame volume, while the overall wrinkled scale increases significantly due to the suppression of the concave structure with CO2 dilution, leading to a decrease of the turbulent flame front area, and subsequently to a decrease of ST/SL.

EGR 가스 폐열회수에 의한 디젤엔진의 연비에 미치는 ATF 워밍업의 영향

Cold start driving cycles exhibit an increases in friction losses due to the low temperatures of metal components and media compared to the normal operating engine conditions. These friction losses are adversely affected to fuel economy. Therefore, in recent years, various techniques for the improvement of fuel economy at cold start driving cycles have been introduced. The main techniques are the upward control of coolant temperature and the fast warm-up techniques. In particular, the fast warm-up techniques are implemented with the coolant flow-controlled water pump and the WHRS (waste heat recovery system). This paper deals with an effect of fast ATF (automatic transmission fluid) warm-up on fuel economy using a recovery system of EGR gas waste heat in a diesel engine. On a conventional diesel engine, two ATF coolers have been connected in series, i.e., an air-cooled ATF cooler is placed in front of the condenser of air conditioning system and a water-cooled one is embedded into the radiator header. However, the new system consists of only a water-cooled heat exchanger that has been changed into the integrated structure with an EGR cooler to have the engine coolant directly from the EGR cooler. The ATF cooler becomes the ATF warmer and cooler, i.e., it plays a role of an ATF warmer if the temperature of ATF is lower than that of coolant, and plays a role of an ATF cooler otherwise. Chassis dynamometer experiments demonstrated the fuel economy improvement of over 2.5% with rapid increase in the ATF temperature.

디젤 저온연소 운전 영역에서 흡기압이 엔진 성능에 주는 영향

One of the effective ways to reduce both <TEX>$NO_x$</TEX> and PM at the same time in a diesel CI engine is to operate the engine in low temperature combustion (LTC) regimes. In general, two strategies are used to realize the LTC operation-dilution controlled LTC and late injection LTC - and in this study, the former approach was used. In the dilution controlled regime, LTC is achieved by supplying a large amount of EGR to the cylinder. The significant EGR gas increases the heat capacity of in-cylinder charge mixture while decreasing oxygen concentration of the charge, activating low temperature oxidation reaction and lowering PM and <TEX>$NO_x$</TEX> emissions. However, use of high EGR levels also deteriorates combustion efficiency and engine power output. Therefore, it is widely considered to use increased intake pressure as a way to resolve this issue. In this study, the effects of intake pressure variations on performance and emission characteristics of a single cylinder diesel engine operated in LTC regimes were examined. LTC operation was achieved in less than 8% <TEX>$O_2$</TEX> concentration and thus a simultaneous reduction of both PM and <TEX>$NO_x$</TEX> emission was confirmed. As intake pressure increased, combustion efficiency was improved so that THC and CO emissions were decreased. A shift of the peak Soot location was also observed to lower <TEX>$O_2$</TEX> concentration while <TEX>$NO_x$</TEX> levels were kept nearly zero. In addition, an elevation of intake pressure enhanced engine power output as well as indicated thermal efficiency in LTC regimes. All these results suggested that LTC operation range can be extended and emissions can be further reduced by adjusting intake pressure.