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Technical Paper

Modeling Three-Way Catalyst Converters During Cold Starts And Potential Improvements

2019-12-19
2019-01-2326
Three-way catalyst (TWC) converters are often used to purify toxic substances contained in exhaust emissions from gasoline engines. However, a large amount of CO, NOx and THC may be emitted before the TWC reaches its light-off temperature during a cold start. In this work, a numerical model was developed for studying the purification performance of a close-coupled TWC converter during the cold start period. The TWC model was built using axisuite, commercial software by Exothermia S.A. Model gas experiments were designed for calibrating the chemical reaction scheme and corresponding reaction rate parameters in the TWC model. The TWC model was able to simulate the purification performance of CO, NOx and THC under both lean and rich air-fuel equivalence ratios (λ) for different conditions. The light-off temperature and oxygen storage capacity (OSC) behavior were also successfully validated in the model. Vehicle tests were conducted on a chassis dynamometer to verify the TWC model.
Technical Paper

Analysis of NH3 Diffusion Phenomena in a Selective Catalytic Reduction Coated Diesel Particulate Filter Catalyst Using a Simple One-Dimensional Core Model

2019-12-19
2019-01-2236
This paper describes a method for estimating constants related to NH3 gas diffusion phenomena to the active sites in a selective catalytic reduction diesel particulate filter (SCR/DPF) catalyst. A simple one-dimensional NH3 gas diffusion model based on the pore structure inside the catalyst was developed and used to estimate the intracrystalline diffusion coefficient. It was shown that the estimated value agreed well with experimental data.
Technical Paper

A Study on Combustion Characteristics of a High Compression Ratio SI Engine with High Pressure Gasoline Injection

2019-09-09
2019-24-0106
In order to improve thermal efficiency of spark ignition (SI) engines, an improved technology to avoid irregular combustion under high load conditions of high compression ratio SI engines is required. In this study, the authors focused on high pressure gasoline direct injection in a high compression ratio SI engine, which its rapid air-fuel mixture formation, turbulence, and flame speed, are enhanced by high-speed fuel spray jet. Effects of fuel injection pressure, injection and spark ignition timing on combustion characteristics were experimentally and numerically investigated. It was found that the heat release rate was drastically increased by raising the fuel injection pressure. The numerical simulation results show that the high pressure gasoline direct injection enhanced small-scale turbulent intensity and fuel evaporation, simultaneously.
Technical Paper

A Fundamental Study on Combustion Characteristics in a Pre-Chamber Type Lean Burn Natural Gas Engine

2019-09-09
2019-24-0123
Pre-chamber spark ignition technology can stabilize combustion and improve thermal efficiency of lean burn natural gas engines. During compression stroke, a homogeneous lean mixture is introduced into pre-chamber, which separates spark plug electrodes from turbulent flow field. After the pre-chamber mixture is ignited, the burnt jet gas is discharged through multi-hole nozzles which promotes combustion of the lean mixture in the main chamber due to turbulence caused by high speed jet and multi-points ignition. However, details mechanism in the process has not been elucidated. To design the pre-chamber geometry and to achieve stable combustion under the lean condition for such engines, it is important to understand the fundamental aspects of the combustion process. In this study, a high-speed video camera with a 306 nm band-pass filer and an image intensifier is used to visualize OH* self-luminosity in rapid compression-expansion machine experiment.
Technical Paper

Analysis and Modeling of NOx Reduction Based on the Reactivity of Cu Active Sites and Brønsted Acid Sites in a Cu-Chabazite SCR Catalyst

2019-09-09
2019-24-0150
The NOx-reducing activity of a Cu-chabazite selective catalytic reduction (SCR) catalyst was analyzed over a wide temperature range. The analysis was based on the ammonia SCR (NH3-SCR) mechanism and accounted for Cu redox chemistry and reactions at Brønsted acid sites. The reduction of NOx to N2 (De-NOx) at Cu sites was found to proceed via different paths at low and high temperatures. Consequently, the rate-limiting step of the SCR reaction at Cu sites varied with the temperature. The rate of NOx reduction at Cu sites below 200°C was determined by the rate of Cu oxidation. Conversely, the rate of NOx reduction above 300°C was determined by the rate of NH3 adsorption on Cu sites. Moreover, the redox state of the active Cu sites differed at low and high temperatures. To clarify the role of the chabazite Brønsted acid sites, experiments were also performed using a H-chabazite catalyst that lacks Cu sites.
Technical Paper

Exhaust Purification Performance Enhancement by Early Activation of Three Way Catalysts for Gasoline Engines Used in Hybrid Electric Vehicles

2019-09-09
2019-24-0148
Three-way catalyst (TWC) converters are used to remove harmful substances (e.g., carbon monoxide (CO), nitrogen oxides (NOx), and hydrocarbons (HC)) emitted from gasoline engines. However, a large amount of emissions could be emitted before the TWC reaches its light-off temperature during a cold start. For hybrid electric vehicles (HEVs) powered by gasoline engines, the emission purification performance by TWC converters unfortunately deteriorates because of mode switching from engine to battery and vice versa, which can repeatedly generate cold start conditions for the TWCs. In this study, aiming to reduce emissions from series HEVs by early activation of TWCs, numerical simulations and experiments are carried out. An HEV is tested on a chassis dynamometer in the Worldwide Light-duty Test Cycle (WLTC) mode. The upstream and downstream gas conditions of the close-coupled catalyst converter are measured.
Technical Paper

Kinetic Modeling of Ammonia-SCR and Experimental Studies over Monolithic Cu-ZSM-5 Catalyst

2019-01-15
2019-01-0024
Ammonia-selective catalytic reduction (SCR) systems have been introduced commercially in diesel vehicles, however catalyst systems with higher conversion efficiency and better control characteristics are required to know the actual emissions during operation and the emissions in random test cycles. Computational fluid dynamics (CFD) is an effective approach when applied to SCR catalyst development, and many models have been proposed, but these models need experimental verification and are limited in the situations they apply to. Further, taking account of redox cycle is important to have better accuracy in transient operation, however there are few models considering the cycle. Model development considering the redox reactions in a zeolite catalyst, Cu-ZSM-5, is the object of the research here, and the effects of exhaust gas composition on the SCR reaction and NH3 oxidation at high temperatures are investigated.
Technical Paper

Effects of Soot Deposition on NOx Purification Reaction and Mass Transfer in a SCR/DPF Catalyst

2018-09-10
2018-01-1707
Experimental studies were carried out to investigate the effect of soot deposition on NOx purification phenomena in an ammonia selective catalytic reduction coated diesel particulate filter (SCR/DPF) catalyst. To study soot deposition effects on the chemical reactions and mass transfer, two types of testing device were used. A synthetic gas bench enabling tests to be conducted with temperature and flow rate ranges relevant to real driving conditions was used to investigate the soot influence on reduction of NOx to N2 (DeNOx). A micro-reactor that removed the effect of soot deposition on mass transfer in the catalyst layer was used to analyze chemical reactions on a soot surface and their interaction with the SCR catalyst. A filter test brick of a Cu-zeolite SCR/DPF catalyst and a powder catalyst were used for the synthetic gas bench and micro-reactor tests, respectively. Engine soot was sampled in all the tests.
Technical Paper

Performance Improvements in a Natural Gas Dual Fuel Compression Ignition Engine with 250 MPa Pilot Injection of Diesel Fuel as an Ignition Source

2016-10-17
2016-01-2306
The engine performance and the exhaust gas emissions in a dual fuel compression ignition engine with natural gas as the main fuel and a small quantity of pilot injection of diesel fuel with the ultra-high injection pressure of 250 MPa as an ignition source were investigated at 0.3 MPa and 0.8 MPa IMEP. With increasing injection pressure the unburned loss decreases and the thermal efficiency improves at both IMEP conditions. At the 0.3 MPa IMEP the THC and CO emissions are significantly reduced when maintaining the equivalence ratio of natural gas with decreasing the volumetric efficiency by intake gas throttling, but the NOx emissions increase and excessive intake gas throttling results in a decrease in the indicated thermal efficiency. Under the 250 MPa pilot injection condition simultaneous reductions in the NOx, THC, and CO emissions can be established with maintaining the equivalence ratio of natural gas by intake gas throttling.
Journal Article

Detailed Diesel Combustion and Soot Formation Analysis with Improved Wall Model Using Large Eddy Simulation

2015-11-17
2015-32-0715
A mixed time-scale subgrid large eddy simulation was used to simulate mixture formation, combustion and soot formation under the influence of turbulence during diesel engine combustion. To account for the effects of engine wall heat transfer on combustion, the KIVA code's standard wall model was replaced to accommodate more realistic boundary conditions. This were carried out by implementing the non-isothermal wall model of Angelberger et al. with modifications and incorporating the log law from Pope's method to account for the wall surface roughness. Soot and NOx emissions predicted with the new model are compared to experimental data acquired under various EGR conditions.
Technical Paper

Development of a Micro-Reactor HC-SCR System and the Evaluation of NOx Reduction Characteristics

2015-09-01
2015-01-2021
To reduce NOx emissions from diesel engines, the urea-SCR (selective catalytic reduction) system has been introduced commercially. In urea-SCR, the freezing point of the urea aqueous solution, the deoxidizer, is −11°C, and the handling of the deoxidizer under cold weather conditions is a problem. Further, the ammonia escape from the catalyst and the generation of N2O emissions are also problems. To overcome these disadvantages of the urea-SCR system, the addition of a hydrocarbon deoxidizer has attracted attention. In this paper, a micro-reactor SCR system was developed and attached to the exhaust pipe of a single cylinder diesel engine. With the micro-reactor, the catalyst temperature, quantity of deoxidizer, and the space velocity can be controlled, and it is possible to use it with gas and liquid phase deoxidizers. The catalyst used in the tests reported here is Ag(1wt%)-γAl2O3.
Technical Paper

Developments of the Reduced Chemical Reaction Scheme for Multi-Component Gasoline Fuel

2015-09-01
2015-01-1808
The reduced chemical reaction scheme which can take the effect of major fuel components on auto ignition timing into account has been developed. This reaction scheme was based on the reduced reaction mechanism for the primary reference fuels (PRF) proposed by Tsurushima [1] with 33 species and 38 reactions. Some pre-exponential factors were modified by using Particle Swarm Optimization to match the ignition delay time versus reciprocal temperature which was calculated by the detailed scheme with 2,301 species and 11,116 elementary chemical reactions. The result using the present reaction scheme shows good agreements with that using the detailed scheme for the effects of EGR, fuel components, and radical species on the ignition timing under homogeneous charge compression ignition combustion (HCCI) conditions.
Technical Paper

Numerical Optimization of Parameters to Improve Thermal Efficiency of a Spark-Ignited Natural Gas Engine

2015-09-01
2015-01-1884
Natural gas is a promising alternative fuel for internal combustion engines because of its clean combustion characteristics and abundant reserves. However, it has several disadvantages due to its low energy density and low thermal efficiency at low loads. Thus, to assist efforts to improve the thermal efficiency of spark-ignited (SI) engines operating on natural gas and to minimize test procedures, a numerical simulation model was developed to predict and optimize the performance of a turbocharged test engine, considering flame propagation, occurrence of knock and ignition timing. The numerical results correlate well with empirical data, and show that increasing compression ratios and retarding the intake valve closing (IVC) timing relative to selected baseline conditions could effectively improve thermal efficiency. In addition, employing moderate EGR ratios is also effective for avoiding knock.
Technical Paper

Improvement of Combustion and Emissions in a Dual Fuel Compression Ignition Engine with Natural Gas as the Main Fuel

2015-04-14
2015-01-0863
Dual fuel combustion with premixed natural gas as the main fuel and diesel fuel as the ignition source was investigated in a 0.83 L, single cylinder, DI diesel engine. At low loads, increasing the equivalence ratio of natural gas to around 0.5 with intake throttling makes it possible to reduce the THC and CO emissions as well as to improve the thermal efficiency. At high loads, increasing the boost pressure moderates the combustion, but increases the THC and CO emissions, resulting in deterioration of the thermal efficiency. The EGR is essential to suppress the rapid combustion. As misfiring occurs with a compression ratio of 14.5 and there is excessively rapid combustion with 18.5 compression ratio, 16.5 is a suitable compression ratio.
Technical Paper

Computational Study to Improve Thermal Efficiency of Spark Ignition Engine

2015-03-10
2015-01-0011
The objective of this paper is to investigate the potential of lean burn combustion to improve the thermal efficiency of spark ignition engine. Experiments used a single cylinder gasoline spark ignition engine fueled with primary reference fuel of octane number 90, running at 4000 revolution per minute and at wide open throttle. Experiments were conducted at constant fueling rate and in order to lean the mixture, more air is introduced by boosted pressure from stoichiometric mixture to lean limit while maintaining the high output engine torque as possible. Experimental results show that the highest thermal efficiency is obtained at excess air ratio of 1.3 combined with absolute boosted pressure of 117 kPa. Three dimensional computational fluid dynamic simulation with detailed chemical reactions was conducted and compared with results obtained from experiments as based points.
Journal Article

Molecular Structure of Hydrocarbons and Auto-Ignition Characteristics of HCCI Engines

2014-11-11
2014-32-0003
The chemical composition of marketed gasoline varies depending on the crude oil, refinery processes of oil refineries, and season. The combustion characteristics of HCCI engines are very sensitive to the fuel composition, and a fuel standard for HCCI is needed for HCCI vehicles to be commercially viable. In this paper, the effects of the structure of the fuel components on auto-ignition characteristics and HCCI engine performance were investigated. The engine employed in the experiments is a research, single cylinder HCCI engine with a compression ratio of 14.7. The intake manifold was equipped with a heater attachment allowing control of the intake air temperature up to 150 °C at 2000 rpm. Thirteen kinds of hydrocarbons, 4 kinds of paraffins, 3kinds of naphthenes, and 6 kinds of aromatics, were chosen for the investigation, and 20vol% of each of the pure hydrocarbons was blended with the 80 vol% of PFR50 fuel.
Technical Paper

Dual Fuel Diesel Combustion with Premixed Ethanol as the Main Fuel

2014-10-13
2014-01-2687
Dual fuel combustion with premixed ethanol as the main fuel and direct injection of diesel fuel as an ignition source poses problems including large unburned emissions and excessively rapid combustion. In this report the influence of compression ratios, injection timings of diesel fuel, and intake oxygen concentrations was systematically investigated in a modern diesel engine. The combustion process was classified into three stages: the first rapid combustion of diesel fuel and the ethanol mixture entrained into the diesel fuel spray; the second mild combustion with flame propagation of the ethanol mixture; and the third rapid combustion with auto-ignition of the unburned ethanol mixture without knocking. The third stage combustion occurs occasionally at several operating conditions and has been termed as PREMIER (premixed mixture ignition in the end-gas region) combustion.
Journal Article

Combustion Characteristics of Emulsified Blends of Water and Diesel Fuel in a Diesel Engine with Cooled EGR and Pilot Injection

2013-10-15
2013-32-9022
Water and diesel fuel emulsions containing 13% and 26% water by volume were investigated in a modern diesel engine with relatively early pilot injection, supercharging, and cooled EGR. The heat release from the pilot injection with water emulsions is retarded toward the top dead center due to the poor ignitability, which enables larger pilot and smaller main injection quantities. This characteristic results in improvements in the thermal efficiency due to the larger heat release near the top dead center and the smaller afterburning. With the 26% water emulsion, mild, smokeless, and very low NOx operation is possible at an optimum pilot injection quantity and 15% intake oxygen with EGR at or below 0.9 MPa IMEP, a condition where large smoke emissions are unavoidable with regular unblended diesel fuel. Heat transfer analysis with Woschni's equation did not show the decrease in cooling loss with the water emulsion fuels.
Journal Article

A Numerical Study of the Effects of FAME Blends on Diesel Combustion and Emissions Characteristics Using a 3-D CFD Code Combined with Detailed Kinetics and Phenomenological Soot Formation Models

2013-10-14
2013-01-2689
The objective of the present research is to analyze the effects of using oxygenated fuels (FAMEs) on diesel engine combustion and emission (NOx and soot). We studied methyl oleate (MO), which is an oxygenated fuel representative of major constituents of many types of biodiesels. Engine tests and numerical simulations were performed for 100% MO (MO100), 40% MO blended with JIS#2 diesel (MO40) and JIS#2 diesel (D100). The effects of MO on diesel combustion and emission characteristics were studied under engine operating conditions typically encountered in passenger car diesel engines, focusing on important parameters such as pilot injection, injection pressure and exhaust gas recirculation (EGR) rate. We used a diesel engine complying with the EURO4 emissions regulation, having a displacement of 2.2 L for passenger car applications. In engine tests comparing MO with diesel fuel, no effect on engine combustion pressure was observed for all conditions tested.
Technical Paper

Identification of Factors Influencing Premixed Diesel Engine Noise and Mechanism of Noise Reduction by EGR and Supercharging

2013-04-08
2013-01-0313
To determine the engine noise reduction methods, an engine noise research was conducted experimentally with a PCCI diesel engine. The engine employed in the experiments was a supercharged, single-cylinder DI diesel engine with a high pressure common rail fuel injection system. The engine noise was sampled by two microphones and the sampled engine noise was averaged and analyzed by an FFT sound analyzer. The engine was equipped with a pressure transducer and the combustion noise was calculated from the power spectrum of the FFT analysis of the in-cylinder pressure wave form and the cross power spectrum of the sound pressure of the engine noise. It is well known that the maximum pressure rise rate is the main parameter related to the engine noise. The PCCI engine was operated at a 1.0 MPa/°CA maximum pressure rise rate to eliminate the effects of the maximum pressure rise rate, and parameters which had the dominant effect on engine noise and combustion noise were determined.
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