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Upon an innovative compact design, extraordinary heat retention capability is demonstrated with a reverse-flow catalytic converter (RFC). By periodical flow reversal, the monolith solid to gas-flow thermal energy recovery, which generates a superior temperature profile oscillating along the monolith flow-path, escalates the temperature-rise by the exothermic reaction of THC and CO. Thus, the averaged temperature level of the catalytic monolith is raised substantially independent of the inflow gas temperature from engine exhaust, while an ordinary flow-through catalyst would lose light off following similar operations with low exhaust temperatures. Along the exhaust flow-path of a typical diesel-dual fuel RFC operation, the monolith center temperature is highly elevated from the boundary temperatures, while the boundary temperatures are approximating the inflow exhaust temperature.

A two-chamber catalyst system for the aftertreatment of No. 2 Diesel exhaust is demonstrated. NOx conversion efficiencies greater than 90% were obtained over a broad range of operating temperatures and NOx levels. The system incorporates a catalyst (SCONOx™) for the removal of CO, hydrocarbons, and NOx from the exhaust stream and a sulfur catalyst (SCOSOx™) for the protection of the NOx catalyst from sulfur poisoning. Both catalysts are of sorbate or “trap” type. No. 2 Diesel and hydrogen were used as reductants. Tests of the catalysts were performed with various loads, temperatures, and NOx levels. A light-duty diesel engine with no particulate control was used for the tests. All tests were conducted using No. 2 Diesel fuel. NOx conversion decay is compared with and without sulfur catalyst protection.

This paper studies the effect of nozzle geometry on the flow characteristics inside a diesel fuel injection nozzle and correlates to the subsequent atomization process under different operating conditions, using simple turbulent breakup model. Two kinds of nozzles, valve covered orifice (VCO) and mini-SAC nozzle, with various nozzle design parameters were studied. The internal flow inside the nozzle was simulated using 3-D computational fluid dynamics software with k-ε turbulence model. The flow field at the nozzle exit was characterized by two parameters: the fuel discharge coefficient Cd and the initial amplitude parameter amp0. The latter parameter represents the turbulence characteristics of the exit flow. The effects of nozzle geometry on the mean velocity and turbulent energy distribution of the exit flow were also studied. The characteristics of the exit flow were then incorporated into the spray model in KIVA-II to study the effect of nozzle design on diesel spray behavior.

A new type of catalyst for exhaust emission control of Diesel engines has been developed by a catalyst producer in cooperation with engine/heavy duty truck manufacturers. This so-called Sorption/Oxidation (“SO”)-catalyst is an extruded TiO2-type and works as a HC-trap as well as oxidation catalyst for hydrocarbons. In addition, a certain amount of particle matter was reduced, depending on type of engine, fuel sulfur content and test cycle. Due to its unique composition, i.e. oxides of titanium (80 wt %), tungsten and vanadium, the catalytic selectivity results in very low formation of sulfates as well as excellent resistance against sulfur compounds. The geometry of the catalyst prototypes corresponds to standard monoliths of 5,66″(144mm) in diameter and suitable lengths to be installed in standard mufflers. Since 1996, several buses and trucks have been equipped with SO-catalysts and are still in operation without problems.

Diesel exhaust gas contains low molecular aliphatic carbonyl compounds and strongly smelling organic acids, which are known to have an irritant influence on eyes, nose and mucous membranes. Thus, diesel exhaust aftertreatment has to be considered more critically than that of gasoline engines, with respect to the formation of undesired by-products. The results presented here have been carried out as research work sponsored by the German Research Association for Internal Combustion Engines (FVV). The main objective of the three year project was to evaluate the behaviour of current and future catalyst technology on the one hand (oxidation catalyst, CRT system, SCR process), and regulated and certain selected non-regulated exhaust gas emission components and exhaust gas odour on the other hand.

A recently developed technique, crossed-plane imaging, is extended to measure instantaneous flamelet surface normals in a single-cylinder, optical SI engine. Two simultaneous, orthogonal acetone PLIF images are used to measure the instantaneous flamelet orientation in three dimensions. The images are also used to measure contours of constant mean reaction progress variable < c> and the mean flamelet crossing density. Statistics of the flamelet surface normal are presented in spherical coordinates in terms of a polar angle, f, and an azimuthal angle,q; the pole is aligned with the normal to a constant surface. The data are used to estimate marginal probability density functions (PDF's) in f and q. The estimated marginal PDF's are found to be well represented by the same functional forms applied previously to turbulent V-flames. The flamelet surface density and the mean fractional increase in flamelet surface area due to turbulence are also estimated.

The early flame kernel development period has a strong influence on the ultimate performance and emission characteristics of spark ignition engines. The fibre-optic instrumented spark plug, FOSP, is a tool used to characterise the early flame kernel development period without the need to modify production engines. Simultaneous in-cylinder pressure, fibre-optic spark plug and secondary ignition system voltage measurements have been made in the GM 2.8 L and the high swirl 3.1 L production engines modified to run on a single cylinder. The secondary ignition system voltages indicate that restrikes are occurring and that spark anemometry is a promising tool to extract information about the flow near the spark plug at the time of ignition. Further development of the technique is, however, required.

The formation of nitric oxide in a transparent direct injection gasoline engine was studied experimentally using two different schemes of laser-induced fluorescence (LIF) with KrF excimer (248 nm) excitation. With detection of the fluorescence shifted towards the red, strong interference from fluorescence of partially burned fuel was found. With blue-shifted fluorescence, interference was minimized allowing selective detection of NO. Possibilities of quantifying NO fluorescence intensities in inhomogeneous combustion are discussed.

Recent measurements of NOx emissions from a 2.2L HSDI Diesel engine have suggested that NO decomposition may be important at high load [1]. In interpretation of these data, Mellor et al. [2] determined that the nitrous oxide and extended Zeldovich mechanisms are both important pathways for NO formation and decomposition. To further examine the importance of NO decomposition in Diesels, results from tests that involve the injection of pure NO into the intake air of a 2.4L HSDI Diesel are presented. The effects of engine speed and load on the relative importance of NO decomposition are directly discernable from graphs of engine–out NOx versus engine–in NO for speed and load sweeps. The importance of NO decomposition is found to increase with engine load, while engine speed exhibits a tradeoff. Furthermore, the results indicate that the reverse of the Zeldovich mechanism dominates the NO decomposition process.

Modern diesel engine injection systems are largely computer controlled. This opens the door for tailoring the fuel rate. Rate shaping in combination with increased injection pressure and nozzle design will play an important role in the efforts to maintain the superiority of the diesel engine in terms of fuel economy while meeting future demands on emissions. This approach to studying the potential of rate shaping in order to reduce NO formation is based on three sub-models. The first model calculates the fuel rate by using standard expressions for calculating the areas of the dimensioning flow paths in the nozzle and the corresponding discharge coefficients. In the second sub-model the heat release rate is described as a function of available fuel energy, i.e. fuel mass, in the cylinder. The third submodel is the multizone combustion model that calculates NO for a given heat release rate under assumed air /fuel ratios.

A major problem in reducing pollutant emissions from diesel engines is the soot-NOx trade-off. With the introduction of the Common-Rail injection system splitting the injection into separate pulses has become possible. Experiments using multiple injections indicated that there is the chance to shift the soot-NOx curve closer to the origin. In order to understand the underlying physical process multidimensional simulations have been carried out for a baseline as well as a split injection case using the Representative Interactive Flamelet (RIF)-Model. The computations are compared to experimental data showing good agreement for both cases. The computations as well as the experiments confirm the possibility of reducing soot with only a slight increase in NOx emissions. It is shown that soot is reduced due to a different mixing process resulting in fewer rich regions.

For studying the effects of injection system properties and combustion chamber conditions on the penetration lengths of both the liquid and the vapor phase of fuel injectors in Diesel engines, a holistic injection model was developed, combining hydraulic and spray modeling into one integrated simulation tool. The hydraulic system is modeled by using ISIS (Interactive Simulation of Interdisciplinary Systems), a one dimensional in–house code simulating the fuel flow through hydraulic systems. The computed outflow conditions at the nozzle exit, e.g. the dynamic flow rate and the corresponding fuel pressure, are used to link the hydraulic model to a quasi–dimensional spray model. The quasi–dimensional spray model uses semi–empirical 1D correlation functions to calculate spray angle, droplet history and droplet motion as well as penetration lengths of the liquid and the vapor phases. For incorporating droplet vaporization, a single droplet approach has been used.

As interest has grown in diesel emissions and diesel engine aftertreatment, so has the importance of analyzing all components of the exhaust. One of the more costly and difficult measurements to make is the collection and analysis of semivolatile organic compounds (SOCs) in the exhaust. These compounds include alkane and alkenes from C12-C24, and the 2-5 ring polycyclic aromatic hydrocarbons (PAH). These compounds can be present in both the particulate (i.e. on the filter) and gaseous phase, and cannot be collected with bag samples. Typically, a sorbent is used downstream of the particulate collection filters to collect these compounds. Sorbent phases include polyurethane foam (PUF), Tenax™, XAD-type resins, and activated carbon. The SOCs are removed from the sorbent either by solvent extraction (PUF and XAD) or thermal desorption (Tenax™ and activated carbon). Each of these methods have advantages and disadvantages.

A model based on Representative Interactive Flamelets (RIF) for simulating ignition, combustion and emissions formation in a DI diesel engine has been applied to describe the combustion process in the Ford DIATA engine. Equipped with a common-rail injection system the four-valve, turbocharged engine with a displacement of 300 cc per cylinder represents a modern HSDI small-bore diesel engine. The RIF-model offers a way of decoupling the turbulent time scales from those associated with the chemistry. The turbulent flow field was solved using the three-dimensional CFD-code KIVA 3V and the chemistry was solved in a one-dimensional flamelet code rendering profiles of species mass fractions as a function of the mixture fraction, which is a conserved scalar. This decoupling enabled a detailed reaction mechanism comprising 118 species and 557 elementary reactions to be employed without imposing a significant penalty on the computational time.

The instantaneous structure of a spark ignition direct injection (SIDI) engine fuel spray and the effect of injection pressure on spray structure have been investigated using flow visualization and digital particle image velocimetry (DPIV). Fuel spray experiments have been performed within a non-motored research cylinder. Instantaneous images of the fuel spray are illuminated using single Nd:YAG laser pulses (3-5 ns pulse width) formed into a sheet and passed through the fuel spray. These images are captured using a digital camera connected to an image acquisition board and computer. Flow visualization experiments for a production DI fuel injector, four injection pressures (2.1, 3.4, 4.8, and 6.2 MPa), and a 2 ms injector pulse width illustrate the evolution and instantaneous flow structure of the dense transient spray as a function of injection pressure.

Two-Dimensional, single-shot spontaneous Raman measurements of methane concentration were performed in an optically accessible engine after direct injection with the use of modified air-assisted injector. The spatial resolution of the measurements was determined by the thickness of the laser sheet which was 0.8 mm. The error in the methane number density measurement was determined by the noise in the intensified camera output and was 16% of pure methane number density at the experimental conditions. Effective suppression of the stray light background was the main experimental difficulty. Satisfactory results were acquired only when the spark plug was substituted by a plug covered with a velvet-like, black piece of cloth. These preliminary results show that, for the specific engine configuration, fast mixing of the charge yields a very mild stratification after the end of injection.

Combined Catalytic Hot Wires Probe (CHWP) and Fuel Air Ratio Laser Induced Exciplex Fluorescence (FARLIEF) techniques have been applied to a Gasoline Direct Injection Engine to characterize temporal and spatial evolution of the fuel/air ratio in the vicinity of the spark plug. The engine ran below stoichiometric with early injection (homogenous case taken as a reference) or late injection timing with a global equivalence ratio as low as 0.3. Under lean and late injection conditions, the temporal CHWP signal indicates that a rich vapor cloud is carried to the vicinity of the spark plug. CHWP and FARLIEF techniques show that the maximum equivalence ratio in the fuel cloud reaching the spark does not depend on the injection duration. Instead, the duration appeared to affect the size of this rich vapor pocket.

The Cambustion fast-response flame ionization detector (FFID) has been successfully used for instantaneous exhaust port hydrocarbon (HC) concentration measurement in IC engines for a decade. Measurements of in-cylinder HC concentration have also been made, but these present greater challenge. As the sample transit time and the time constant of the system always change when the sampling pressure is changed, it is necessary to investigate the characteristics of the system before it was used for in-cylinder sampling. A unique method was designed to study the influence of the diameter and length of the transfer sample line and the operating parameters of the FFID on the transit time and time constant. A database of transit time and time constant was built up for different simulated in-cylinder pressures. The database can be used for correcting eventual in-cylinder HC concentration measurement.

Two-dimensional cycle-resolved burnt gas temperatures were measured using two line atomic fluorescence (TLAF) in a single cylinder spark ignition car engine. Mapping of the in-cylinder flow was done under the same operating conditions using Particle Imaging Velocimetry (PIV). Experimental data for temperature and flow was compared to results from numerical simulations.

This paper presents an investigation of a Volvo Direct Injection Spark Ignition (DISI) engine, where the fuel distribution and the in-cylinder flow field have been mapped by the use of laser techniques in an engine with optical access. Along with the experimental work, CFD-modelling of flow and fuel distribution has been performed. Laser Induced Fluorescence (LIF) visualisation of the fuel distribution in a DI-engine has been performed using an endoscopic detection system. Due to the complex piston crown geometry it was not possible to monitor the critical area around the sparkplug with conventional, through the piston, detection. Therefore, an endoscope inserted in the spark plug hole was used. This approach gave an unrestricted view over the desired area. In addition, the in-cylinder flow fields have been monitored by Particle Image Velocimetry (PIV) through cylinder and piston. The results from both the LIF and the PIV measurements have been compared with CFD-modelling at Volvo.