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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.

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.

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.

The objective of the present research is to investigate the effects on diesel engine combustion and NOx and PM emission characteristics in case of blending the ordinary diesel fuel with biodiesel in passenger car diesel engines. Firstly, we conducted experiments to identify the combustion and emissions characteristics in a modern diesel engine complying with the EURO 4 emission standard. Then, we developed a numerical simulation model to explain and generalize biodiesel combustion phenomena in detail and generalize emission characteristics. The experimental and simulation results are useful to reduce biodiesel emissions by controlling engine operating and design parameters in the diesel engine. Engine tests were conducted and a mathematical model created to investigate the effects of 40% and 100% methyl oleate modeled fuel representing Jatropha-derived biodiesel on diesel combustion and emission characteristics, over a wide range of passenger car DI diesel engine operating conditions.

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.

Model based control design is an important method for optimizing engine operating conditions so as to simultaneously improve engines' thermal efficiency and emission profiles. Modeling of intake system that includes an intake throttle valve, an EGR valve and a variable geometry turbocharger was constructed based on conservation laws combined with maps. Calculated results were examined the predictive accuracy of fresh charge mass flow, EGR rate and boost pressure.

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%.

From the viewpoint of the global warming restraint, reduction of exhaust emissions from diesel engine is urgent demand. However, it needs further development in combustion control besides after treatment system. Larger amount of EGR (Exhaust Gas Recirculation) is effective to reduce NOx emission. On the other hand, in-cylinder physical conditions greatly influence on self-ignition and combustion process, especially low O2 fraction charged gas owing to excessive EGR causes misfire. A drastic solution for this problem, fuel injection timing should be optimally manipulated based on predicted ignition delay period before actual injection. For this purpose, Toyota has developed a model based diesel combustion control concept to avoid the misfire and to keep low emission combustion includes in transient condition.

We have developed a novel engine cycle simulation program (UniDES: universal diesel engine simulator) to reproduce the diesel combustion process over a wide range of engine operating parameters, such as the amount of injected fuel, the injection timing, and the EGR ratio. The approach described in this paper employs a zoning model, where the in-cylinder region is divided into up to five zones. We also applied a probability density function (PDF) concept to each zone to consider the effect of spatial non-homogeneities, such as local equivalence ratios and temperature, on the combustion characteristics. We linked this program to the commonly used commercial GT-Power® software (UniDES+GT). As a result, we were able to reproduce transient engine behavior very accurately.

In a Diesel Oxidation Catalyst (DOC) and Catalyzed Soot Filter (CSF) system, the DOC is used to oxidize additional fuel injected into the cylinder and/or exhaust pipe in order to increase the CSF's inlet temperature during soot regeneration. The catalyst's hydrocarbon (HC) oxidation performance is known to be strongly affected by the HC species present and the catalyst design. However, the engine operating conditions and additive fuel supply parameters also affect the oxidation performance of DOCs, but the effects of these variables have been insufficiently examined. Therefore, in this study, the oxidation performance of a DOC was examined in experiments in which both exhaust gas recirculation (EGR) levels and exhaust pipe injection parameters were varied. The results were then analyzed and optimal conditions were identified using modeFRONTIER.

For diesel emission control systems containing a Diesel Oxidation Catalyst (DOC) and a Catalyzed Soot Filter (CSF) the DOC is used to oxidize the additional fuel injected into the cylinder and/or the exhaust pipe for the purpose of increasing the CSF inlet temperature during the soot regeneration. Hydrocarbon (HC) oxidation performance of the DOC is affected by HC species as well as a catalyst design, i.e., precious metal species, support materials and additives. How engine-out HC species vary as a function of fuel supply conditions is not well understood. In addition, the relationship between catalyst design and oxidation activity of different hydrocarbon species requires further study. In this study, diesel fuel was supplied by in-cylinder, post injection and exhaust HC species were measured by a gas chromatograph-mass spectrometry (GC-MS) and a gas analyzer. The post injection timing was set to either 73°, 88° or 98° ATDC(after top dead center).

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.

A dual fuel natural gas diesel engine suffers from remarkably lower thermal efficiency and higher THC, CO emissions at lower load because of its lower burned mass fraction caused by the lean pre-mixture. To overcome this inevitable disadvantage at lower load, two methods of reducing the number of operating cylinders were examined. One method was to use the two cylinders operation while the second one was to use the quasi-two cylinders operation. As a result, it was found that the unburned hydrocarbons and CO emissions could be favorably reduced with the improvement of thermal efficiency by reducing the number of cylinders to half for a dual fuel natural gas diesel engine. Moreover, it was also found that the quasi-two cylinders operation could improve the torque fluctuation more compared to the two cylinders operation.

To improve urban air pollution, stringent emissions regulations for heavy-duty diesel engines have been proposed and will become effective in Japan, the EU, and the United States in a few years. To comply with such future regulations, it is critical to investigate the effects of intake and injection parameters and fuel properties on engine performance, efficiency and emissions characteristics, associated with the use of aftertreatment systems. An experimental study was carried out to identify such effects. In addition, the KIVA-3 code was used to gain insight into cylinder events. The results showed improvements in NOx-Smoke and BSFC trade-offs at high-pressure injection in conjunction with EGR and supercharging.

Natural gas pre-mixture is ignited by a small amount of pilot fuel in the dual fuel engine. In this paper, numerical studies were carried out to investigate the combustion and exhaust gas emissions formation process of this engine type by using a multi dimensional model combined with the detailed chemical kinetics including 57 chemical species and 290 elementary reactions. In calculation, the effect of the pre-mixture concentration on combustion was examined. The result indicated that the increased concentration of natural gas could improve the burning fraction and THC, CO emissions due to the increased pre-mixture consumption rate and the cylinders gas temperature.

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.

An experimental and numerical study has been conducted on the emission and reduction of HCHO (formaldehyde) and other pollutants formed in the cylinder of a direct-injection diesel engine fueled by methanol. Engine tests were performed under a variety of intake conditions including throttling, heating, and EGR (exhaust gas recirculation) for the purpose of improving these emissions by changing gas compositions and combustion temperatures in the cylinder. Moreover, a detailed kinetics model was developed and applied to methanol combustion to investigate HCHO formation and the reduction mechanism influenced by associated elementary reactions and in-cylinder mixing.

An experimental study was conducted to determine combustion and exhaust emissions characteristics in an automotive direct-injection diesel engine dual-fueled with natural gas with the objective of improving exhaust emissions and thermal efficiency. Dual-fuel operation can yield a high thermal efficiency almost comparable to the diesel operation and very low smoke at higher loads. However, NOx cannot be reduced by dual-fueling. On the other hand, at lower loads, a dual-fueled engine inevitably suffers from lower thermal efficiency and higher unburned fuel. To resolve these problems, the effects of exhaust gas recirculation (EGR) were investigated. The results show that in dual-fuel operation, hot EGR can improve thermal efficiency and reduce unburned fuel emission at lower loads, While cooled EGR can considerably reduce NOx at higher loads. A Pt oxidation catalyst can be used for additional reduction in unburned fuel emitted due to dual-fueling.