Exhaust Gas Recirculation Gas Research Articles

Impact of Ethylene and NO Addition on Fuel Oxidation Under Simulated HCCI Conditions

We present an investigation on the chemical influence of some exhaust gas recirculation (EGR) compounds on fuel oxidation, especially the effects of NO and ethylene. Two experimental setups were used: a homogeneous charge compression ignition (HCCI) engine and a jet-stirred reactor (JSR). The first one was chosen for its representativeness and the second one for its well-controlled operating conditions. NO and ethylene were selected because NO is known for its high reactivity and ethylene has a high concentration in the EGR gases. A complex impact of NO and little influence of C2H4 on the fuel oxidation kinetics were observed, in accordance with the literature. However, a synergistic effect on fuel oxidation was observed by coupling between NO and ethylene chemistry. For the fuel oxidation, a considerable inhibition at low temperatures and a significant promotion at higher temperatures were observed. These results tend to demonstrate the importance of taking into account the complexity of EGR composition.

Comparison of thermal, radical and chemical effects of EGR gases using availability analysis in dual-fuel engines at part loads

Dual-fuel engines at part load inevitably suffer from lower thermal efficiency and higher emission of carbon monoxide and unburned fuel. A quasi-two-zone combustion model has been developed for studying the second-law analysis of a dual-fuel (diesel–gas) engine operating under part-load conditions. The model is composed of two divisions: a single-zone combustion model with chemical kinetics for combustion of natural gas fuel and a subsidiary zone for combustion of pilot fuel. In the latter zone, the pilot fuel is considered as a heat source derived from two superposed Wiebe’s combustion functions to account for contribution of pilot fuel in ignition of gaseous fuel and the rest of the total released energy. This quasi-two-zone combustion model is able to establish the development of combustion process with time and associated important operating parameters, such as pressure, temperature, heat release rate (HRR) and species concentration. The present work is an attempt to investigate the combustion phenomenon from second-law point of view at part load and using exhaust gas recirculation (EGR) to improve the aforementioned problems. Therefore, the availability analysis is applied to the engine from inlet valve closing (IVC) until exhaust valve opening (EVO). Various availability components are identified and calculated separately with crank position. In this paper, the various availability components are identified and calculated separately with crank position. Then the different cases of EGR (chemical, radical and thermal cases) are applied to the availability analysis in dual-fuel engines at part loads. It is found that the chemical case of EGR has negative effect and in this case the unburned chemical availability is increased and the work availability decreases in comparison with baseline engine (without EGR). While the thermal and radical cases have positive effects on the availability terms especially on the unburned chemical availability and work availability. The results show that second-law efficiency is increased by using low amount of radical and thermal cases of EGR. Implications are discussed in detail.

English

The main aim of this project is to investigate the effects of hot and cold Exhaust gas recirculation (EGR) methods on emissions and efficiency of the single cylinder, 4-stroke, direct injection diesel engine. For getting different EGR methods heat exchanger is provided. With and without Exhaust gas recirculation the performance characteristics like efficiencies, emissions were studied. In this project the different amounts of EGR like 10%, 15% and 20% of EGR is used to study the effects on the performance characteristics The recirculation of exhaust gas reduces the oxygen quantity in the combustion chamber and increases the temperature of intake charge which reduces the flame temperature and makes to lower NOx formation. By increasing the cooled EGR rates reduces the emissions more effectively. Experimental results shows that the cold EGR is much effective than the hot and intermediate EGR for the reduction of NOx emission. The increase in temperature of EGR gases causes to increase the combustion temperature which leads to increase in formation of NOx.

Numerical studies on the mixing characteristics of exhaust gas recirculation gases with air, and their dependence on system geometries in four-cylinder engine applications

To achieve low nitrogen oxide (NO x) emissions and combustion reliability, the variation in the geometry of the exhaust gas recirculation (EGR) system should be optimized. However, the layout process essentially fixes the position of a conventional EGR system, and modifying the intake manifold geometry tends to be economically unjustifiable for a commercial engine. In the present study, two types of EGR system, namely ‘linked single’ and ‘individual’ EGR systems, are proposed and their performances are evaluated numerically. Parametric studies were performed using a three-dimensional numerical model to assess the mixing uniformity of the intake air and EGR gases. The distribution of the mixed gases into the four runners, which force the mixed gases into the four combustion cylinders, is predicted. Three different geometries of the EGR system are considered: single, side-feed individual, and top-feed individual configurations. These geometries reflect the means by which the EGR gases are supplied into the four cylinders. These three configurations are called cases A, B, and C respectively, and their corresponding detailed geometries are identified as A1 to A9, B1 to B17, and C1 to C10, which give a total of 36 computational runs. It was found that case A5 with a hole angle of 60° yielded the most optimal operating mixing and distribution condition. In general, the single systems were found to be superior to the individual systems, among which the top-feed system tended to be slightly more advantageous for mixing than the side-feed individual system owing to the symmetric supply of the top-feed system. The flow of the throttle-valve system, which controls the mass flowrate of the intake air, was used as the validation case; Hyundai-Kia Motor Co. provided the experimental data, which were compared with the computational results.

Impact of acetaldehyde and NO addition on the 1-octene oxidation under simulated HCCI conditions

Due to more and more stringent restrictions on vehicle exhaust emissions, low temperature combustion in automotive engines becomes more and more important. Low temperature combustion is achieved by high rates of Exhaust Gas Recirculation (EGR). EGR gases are used to dilute the fuel/air mixture in the engine and to control ignition delay times. However, nowadays, EGR is also supposed to have chemical impact on the Homogeneous Charge Compression Ignition (HCCI) engine combustion. First, the effects of NO and acetaldehyde addition were studied performing HCCI engine experiments with different concentrations of NO and CH 3CHO. Since the impact of EGR compounds on engine control is difficult to understand in an engine itself, experiments were performed in a Jet-Stirred Reactor (JSR) where conditions are well-controlled. The effects of the addition of NO (100 ppm) and acetaldehyde (200 ppm) on 1-octene oxidation were studied at 1.013 MPa, under dilute conditions. According to the literature, a complex impact of NO was observed, but in contrast to the assumption that aldehydes could have a strong impact on oxidation kinetics, only moderate effects of acetaldehyde were found but leading to a significant impact on combustion in an HCCI engine. However, a synergy between NO and acetaldehyde on the oxidation of 1-octene was observed when these species were added simultaneously leading to an inhibition of fuel oxidation at low temperatures, an important reduction of the NTC-effect, and a promotion of fuel oxidation in higher temperatures. These results tend to demonstrate the importance of taking into account the complexity of EGR composition.

The trapping system for the recirculated gases at different locations of the exhaust gas recirculation (EGR) pipe of a homogeneous charge compression ignition (HCCI) engine

Nowadays, in diesel engines, it is typical to recycle exhaust gases (EGR) in order to decrease pollutant emissions. However, few studies report the precisely measured composition of the recycled gases. Indeed, in order to know precisely the composition of the EGR gases, they have to be sampled hot and not diluted, in contrast to the usual practice. Thus, a new system to collect such samples was developed. With this new trapping system, it is possible to measure the concentrations of NOx, CO, CO2, O2, hydrocarbons (HCs) in the range C1–C9, aldehydes, ketones and PAHs. The trapping system and the analytical protocol used are described in this paper.

Air fraction estimation for multiple combustion mode diesel engines with dual-loop EGR systems

This paper describes an innovative air fraction estimation method for diesel engines with dual-loop exhaust gas recirculation (EGR) systems to conduct multiple and alternative combustion modes for engine-out emission reduction. An observer is designed to estimate the air fractions in all the engine intake/exhaust sections using standard sensors equipped on the engine. The observer can provide indispensable information for the engine controller to exercise closed-loop control on in-cylinder conditions as well as control the in-cylinder high-pressure EGR gas and low-pressure EGR gas amounts, respectively, which are crucial for engines running alternative combustion modes with dual-loop EGR systems. The convergence stability of the observer is proved based on a Lyapunov analysis assisted by physical insights into the engine/combustion systems. The observer is also experimentally validated on a modern light-duty diesel engine with a dual-loop EGR system.

Combustion Control by EGR Management and Cyclic Dispersion Analysis of a HCCI Engine

Homogeneous Charge Compression Ignition (HCCI) engines could offer low NOx, PM emissions and high efficiency. However the operation region is limited because of knocking and misfire. Moreover the HCCI principal lacks direct combustion control and needs a system to control the combustion phasing with high accuracy. Cyclic dispersion is also a big problem in HCCI combustion. Today there exists various ways to control the HCCI combustion but these systems are heavy and complex. In this study, in order to develop a small and light HCCI engine, a simple HCCI combustion control system is proposed. DME (Di-methyl Ether) is used as a fuel to keep the structure small and light. This system uses throttles to change the mixing ratio of stoichiometric pre-mixture. hot EGR (Exhaust Gas Recirculation) gas and cold EGR gas. With this system, combustion control concept is evaluated and characteristics of cyclic dispersion are analyzed experimentally. Moreover, based on these results, reduction of cyclic dispersion is attempted by combustion control.

Effect of exhaust gas recirculation (EGR) temperature for various EGR rates on heavy duty DI diesel engine performance and emissions

DI diesel engines are well established today as the main powertrain solution for trucks and other relevant heavy duty vehicles. At the same time emission legislation (mainly for NOx and particulate matter) becomes stricter, reducing their limit to extremely low values. One efficient method to control NOx in order to achieve future emissions limits is the use of rather high exhaust gas recirculation (EGR) rates accompanied by increased boost pressure to avoid the negative impact on soot emissions. The method is based on the reduction of gas temperature level and O2 availability inside the combustion chamber, but unfortunately it has usually an adverse effect on soot emissions and brake specific fuel consumption (bsfc). The use of high EGR rates creates the need for EGR gas cooling in order to minimize its negative impact on soot emissions especially at high engine load were the EGR flow rate and exhaust temperature are high. For this reason in the present paper it is examined, using a multi-zone combustion model, the effect of cooled EGR gas temperature level for various EGR percentages on performance and emissions of a turbocharged DI heavy duty diesel engine operating at full load. Results reveal that the decrease of EGR gas temperature has a positive effect on bsfc, soot (lower values) while it has only a small positive effect on NO. As revealed, the effect of low EGR temperature is stronger at high EGR rates.

Comparison of thermal and radical effects of EGR gases on combustion process in dual fuel engines at part loads

Dual fuel engines at part load inevitably suffer from lower thermal efficiency and higher emission of carbon monoxide and unburned fuel. This work is conducted to investigate the combustion characteristics of a dual fuel (Diesel–gas) engine at part loads using a single zone combustion model with detailed chemical kinetics for combustion of natural gas fuel. In this home made software, the presence of the pilot fuel is considered as a heat source that is deriving form two superposed Wiebe’s combustion functions to account for its contribution to ignition of the gaseous fuel and the rest of the total released energy. The chemical kinetics mechanism consists of 112 reactions with 34 species. This combustion model is able to establish the development of the combustion process with time and the associated important operating parameters, such as pressure, temperature, heat release rate (HRR) and species concentration. Therefore, this work is an attempt to investigate the combustion phenomenon at part load and using exhaust gas recirculation (EGR) to improve the above mentioned problems. Also, the results of this work show that each of the different cases of EGR (thermal, chemical and radical cases) has an important role on the combustion process in dual fuel engines at part loads. It is found that all the different cases of EGR have positive effects on the performance and emission parameters of dual fuel engines at part loads despite the negative effect of some diluent gases in the chemical case, which moderates too much the positive effects of the thermal and radical cases of EGR. Predicted values show good agreement with corresponding experimental values over the whole range of engine operating conditions. Implications will be discussed in detail.

Effects of CO 2 dilution on turbulent premixed flames at high pressure and high temperature

Turbulent premixed flames of mixtures of CH 4 and air diluted with CO 2 at high pressure and high temperature were experimentally studied to clarify the effects of exhaust gas recirculation (EGR), especially the effects of CO 2 in EGR gases, on turbulent flame characteristics. The maximum CO 2 dilution ratio, defined as the ratio of the molar fraction of CO 2 to those of air and CO 2, was 0.1. The mixture was preheated up to 573 K and the maximum pressure was 1.0 MPa. Bunsen-type turbulent premixed flames of the mixtures were stabilized in a high-pressure chamber. OH-PLIF visualizations of the flames were performed. By analyzing the OH-PLIF images, turbulent burning velocity, mean volume of turbulent flame region, and mean fuel consumption rate were calculated. Results showed that the turbulent burning velocity, S T, normalized using laminar burning velocity, S L, became smaller when the mixture was diluted with CO 2. When the turbulent flame region was defined as the region between 〈 c〉 = 0.1 and 〈 c〉 = 0.9, the mean volume of the flame region increased in the case of CO 2 dilution. Moreover, the mean fuel consumption rate in the flame region decreased with increasing CO 2 dilution ratio. This effect was stronger than the decrease in mass fraction of fuel due to CO 2 dilution. The decrease in the smallest wrinkling scale of the flame front with increasing turbulence Reynolds number in the case of CO 2 dilution was more significant than that in the case of no CO 2 dilution, corresponding well to the scale relation due to turbulence and intrinsic flame instability proposed previously. These results, as well as the previously reported effects of the profiles of the heat-release region on combustion oscillation, imply that exhaust gas recirculation for high-pressure, high-temperature turbulent premixed flames is effective for restraining combustion oscillation of premixed-type gas-turbine combustors.

Development of an Exhaust Gas Recirculation Distribution Prediction Method Using Three-Dimensional Flow Analysis and Its Application

A multidimensional computational fluid dynamics (CFD) method has been used to improve the exhaust gas recirculation (EGR) distribution in the intake manifold. Since gas flow in the intake system is affected by intake pulsation caused by the gas exchange process, a pulsation flow simulation is used. A one-dimensional gas exchange calculation is combined with three-dimensional intake gas flow calculation to simulate pulsation flow. This pulsation flow simulation makes it possible to predict the EGR distribution. The gas flow in the intake system was analyzed in detail. It was found that a reverse flow region formed downstream of the throttle valve. The size and shape of the reverse flow region greatly depend on the engine operating conditions. With a conventional EGR system, it is difficult to distribute EGR uniformly under various engine operating conditions. A new EGR system that uses a spiral flow to mix the fresh air and EGR gas has been developed to obtain a uniform EGR distribution. As a result of adopting this system, a uniform EGR distribution is obtained regardless of the engine operating conditions. This spiral flow EGR system was applied to a low-emission vehicle (LEV) put on the Japanese market.

Autoignition and Combustion of n-Butane/Air Mixtures in Homogeneous Charge Compression Ignition Engine. Effects of Internal EGR on Auto Ignition and Combustion.

In this study, effects of internal EGR ratio on the ignition and the combustion of homogeneous charge compression ignition (HCCI) engine are investigated experimentally. At first, using single cylinder test engine, relation between exhaust valve close timing and internal EGR (Exhaust Gas Re -circulation) ratio is clarified. Effects of an internal EGR gas on autoignition timing, combustion duration and knocking limits are discussed. As a result of an experiment, it became clear the following facts ; with advancing exhaust valve close timing, i) internal EGR ratio is increasing, ii) both knocking limits at high load and misfiring limits at low load are expanding, iii) ignition timing is advancing, iv) combustion duration is decreasing and v) combustion efficiency is increasing.