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The efficiency of the NOx Storage and Reduction (NSR) catalysts used in the aftertreatment of diesel engine exhaust gases can potentially be increased by using reactive reductants such as CO and H₂ that are formed during in-cylinder combustion. In this study, a multi-dimensional computational fluid dynamics (CFD) code coupled with complex chemical analysis was used to study combustion with various fuel after-injection patterns. The results obtained will be useful in designing fuel injection strategies for the efficient formation of CO.

This paper aims to validate chemical kinetic mechanisms of surrogate gasoline three components fuel by calculating one-dimensional laminar burning velocity of iso-octane/air mixture. Next, the application of level-set method on premixed combustion without consideration the effect of turbulence eddies on flame front is also studied in three-dimensional computational fluid dynamic (3D-CFD) simulation. In the 3D CFD simulation, there is an option to calculate laminar burning velocity by using empirical correlations, however it is applicable only for particular initial pressure and temperature in spark ignition engine cases. One-dimensional burning velocities from lean to rich of iso-octane/air mixture are calculated by using CHEMKIN-PRO with detailed chemistry and transport phenomena as a function of different equivalence ratios, different unburnt temperature and pressure ranges.

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.

The purpose of this paper is to build up a model for predicting turbulent burning velocity which can be used for One-Dimensional (1D) engine simulation. This paper presents the relationship between turbulent burning velocity, the Karlovitz number, and the Markstein number for building up the prediction model. The turbulent burning velocity was measured using a single-cylinder gasoline engine, which has an external Exhaust Gas Recirculation (EGR) system. In the experiment, various engine operating parameters, e.g. engine loads and EGR rates, and various engine specifications, i.e. different types of intake ports were tested. The Karlovitz number was calculated using Three-Dimensional Computational Fluid Dynamics (3D-CFD) and detailed chemical kinetics simulation with a premixed laminar flame model. The Markstein number was also calculated using detailed chemical kinetics simulation with the Extinction of Opposed-flow Flame model.

This paper describes the development of an integrated simulation model for evaluating the effects of electrically heating the three-way catalyst (TWC) in a series hybrid electric vehicle (s-HEV) on fuel economy and exhaust gas purification performance. Engine and TWC models were developed in GT-Power to predict exhaust emissions during transient operation. These models were validated against data from vehicle tests using a chassis dynamometer and integrated into an s-HEV model built in MATLAB/Simulink. The s-HEV model accurately reproduced the performance characteristics of the vehicle’s engine, motor, generator, and battery during WLTC mode operation. It can thus be used to predict the fuel consumption, emissions, and performance of individual powertrain components. The engine combustion characteristics were reproduced with reasonable accuracy for the first 50 combustion cycles, representing the cold-start condition of the driving mode.

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.

A numerical study was carried out to investigate combustion characteristics of a dual-fuel gas diesel engine, using a multi-dimensional model combined with detailed chemical kinetics, including 43 chemical species and 173 elementary reactions. In calculations, the effects of initial temperature, EGR ratios on ignition, and combustion were examined. The results indicated EGR combined with intake preheating can favorably reduced NOx and THC emissions simultaneously. This can be explained by the fact that combustion mechanism is changed from flame propagation to HCCl like combustion.

A CFD code combined with detailed chemical kinetics has been developed, linking with KIVA-3 and subroutines in CHEMKIN-II directly with some modifications. By using this CFD code, formation processes of combustion and exhaust gas emission for a turbo-charged DI diesel engine with common rail fuel injection system were simulated. As a result, formation processes of pollutant including NOx and soot were also considered according to the calculation results. The results show that NO caused by the extended Zeldvich mechanism accounted for about 88% of all NO, and it was found that there is a possibility to predict where and when soot will be formed by considering a simplified soot formation model.

A three-dimensional computational fluid dynamics (3D-CFD) code was combined with a detailed combustion chamber heat transfer model. The established model allowed not only prediction of instantaneous combustion chamber wall surface temperature distributions in practical calculation time but also investigation of the characteristics of combustion, emissions and heat losses affected by the wall temperature distributions. Although zero-dimensional combustion analysis can consider temporal changes in the heat transfer coefficient and in-cylinder gas temperature, it cannot take into account the effect of interactions between spatially distributed charge and wall temperatures. In contrast, 3D-CFD analysis can consider temporal and spatial changes in both parameters. However, in most zero-/multi- dimensional combustion analyses, wall temperatures are assumed to be temporally constant and spatially homogeneous.

We have constructed a quasi-2-dimensional NH₃-SCR model with detailed surface reactions to analyze the NOx conversion mechanism and reasons for its inhibition at low temperatures. The model consists of seven detailed surface reactions proposed by Grozzale et al., and calculates longitudinal gas flow, gas phase-catalyst phase mass transfer, and mass diffusion within the catalyst phase in the depth dimension. Using the model, we have analyzed the results of pulsed ammonia (NH₃) feed tests at various catalyst temperatures, and results show that ammonium nitrate (NH₄NO₃) is the inhibitor in NH₃-SCR reactions at low temperatures. In addition, we found that cutting the supply of NH₃ causes decomposition of NH₄NO₃, providing surface ammonia (NH₄+), which rapidly reacts with adjacent NOx, leading to an instantaneous rise in nitrogen (N₂) formation.

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.

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.

Emission regulations are becoming tighter, and Real Driving Emissions (RDE) is proposed as a testing cycle for evaluating modern engine emissions under a wide operation range. For this reason, engine manufacturers have been developing a method to effectively assess engine performances and emissions under a wide range of transient conditions. Transient engine performances can be evaluated efficiently by applying time-series data created by chirp signals. However, when the time-series data produced by the chirp signal are used directly, the engine hardware may damage, and emission performances deteriorate drastically. It is therefore essential to develop a method to avoid these undesirable operating conditions. This work aims to develop an algorithm to avoid such unrealistic operation conditions for engine performance evaluation. A virtual diesel engine (VDE) model is developed based on a four-cylinder engine using GT-POWER software.

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.

Urea-SCR system has a high NOx reduction potential in the steady-state diesel engine operation. In complicated transient operations, however, there are certain problems with the urea-SCR system in that NOx reduction performance degrades and adsorbed NH3 would be emitted. Here, optimum urea injection methods and exhaust bypass control to overcome these problems are studied. This exhaust bypass control enables NO/NOx ratio at the inlet of SCR catalyst to be decreased widely, which prevents over production of NO2 at the pre-oxidation catalyst. Steady-state and simple transient engine tests were conducted to clarify NOx reduction characteristics when optimum urea injection pattern and exhaust bypass control were applied. In simple transient test, only the engine load was rapidly changed for obtaining the fundamental knowledge concerning the effect of those techniques.

Three-way catalyst (TWC) converters can purify harmful substances, such as carbon monoxide, nitrogen oxides, and hydrocarbons, from the exhaust gases of gasoline engines. However, large amounts of these substances may be emitted before the TWC reaches its light-off temperature during cold starts, and its performance may be impaired by thermal deterioration during high-load driving. In this work, a simulation model was developed using axisuite commercial software by Exothermia S.A to predict the light-off conversion performance of Pd/CeO2-ZrO2-Al2O3 catalysts with different degrees of thermal deterioration. The model considered detailed surface reactions and the main factor of the deterioration mechanism. In the detailed reaction mechanism, adsorption, desorption, and surface reactions of each gas species at active sites of the platinum group metal (PGM) particles were considered based on the Langmuir-Hinshelwood mechanism.

Difference of engine combustion characteristics, species and amount of exhaust gas and PM (particulate matter consisted of SOF and Soot and Ash), and especially PM oxidation characteristics were studied when diesel fuel or bio-fuel, here PME (palm oil methyl ester) as an example, was used as a fuel. The fueling rate was adjusted to obtain the same torque for both fuels and engine was operated under several range of EGR (Exhaust Gas Recirculation) ratio. Under such conditions, PME showed shorter ignition delay time and lower R.H.R (rate of heat release) under 0-40% EGR ratio. With respect to engine exhaust gas species, CO, NO, THC and HCHO, CH3CHO concentration was almost the same when the EGR ratio is higher than 35% (Intake-Air/Fuel: A/F=20). However, PME also showed lower exhaust gas emission when the EGR ratio is higher than 30%.

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.

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.

Swirl injector spray at high fuel temperatures has unique characteristics [1][2][3][4] compared to normal fuel temperature spray such as strong penetration and narrow spray width. These characteristics have a possibility for improving fuel consumption and exhaust emission at the cold start condition. Thus, Swirl injector spray at high fuel temperature conditions was modeled in a CFD(Computational Fluid Dynamics) code by using a multi components fuel evaporation model and other spray sub-models to predict the mixture formation process at the cold start condition. Results show that, high temperature fuel decreases wall film amount and increases vapor amount. It can be concluded that high temperature fuel has the possibility for improving fuel consumption and exhaust emission at the cold start condtion.