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This paper describes an experimental study comparing the peak ignition voltage requirements of natural gas and gasoline in a typical bi-fuel vehicle application. Chassis dynamometer tests were carried out in which the vehicle was subjected to different types of transient wide open throttle events to create “worst case” voltage requirements. In addition to measurements of ignition voltage, other factors known to influence voltage requirements (such as cylinder pressure, electrode temperature, and fuel/air ratio) were recorded during the transient tests in order to obtain a better understanding of the underlying reasons for observed differences in voltage requirements between the two fuels and between the different transient test procedures. The results presented in this paper quantify the increased peak voltage requirements (relative to gasoline) for reliable ignition of natural gas under various operating conditions.

It has been found in the experiments [1], that fuel injection timings, ignition delays, and, thus, the mixture composition at the moment of auto-ignition had a considerable impact on soot formation in a constant volume at Diesel-like conditions. At increased ambient temperatures, soot formation started earlier and higher soot mass concentrations were registered during combustion. Increasing air pressures lead to a slight increase of the mass of soot formed. Nearly no difference of the maximum soot mass concentration has been observed, albeit the time period, in which soot was detected at a certain position increases with the ambient pressure increase. As observed in more resent experiments [2], a variation of the injected fuel quantity has been in an evident fashion related with the amount of soot produced with an exception that less soot yield has been confirmed when the injection time was simultaneously reduced.

In this paper, we report direct calculations of cavitating pipe flows by the method of Space-Time Conservation Element and Solution Element, or the CE/SE method for short. The tenet of the CE/SE method is treating space and time as one entity, and the calculation of flow properties is based on the local and global space-time flux conservation. As a contrast to the modern upwind schemes, no Riemann solver is used, thus the logic of the present scheme for cavitating flows is much simpler. Two numerical examples are reported in this paper: (1) a hydraulic shock problem, and (2) a cavitating pipe flow. For the hydraulic shock problem, we demonstrate the capability of the CE/SE method for capturing contact discontinuities in cavitating fluids. For the pipe flows, a two-phase homogeneous equilibrium cavitation model is employed. In both cases, numerical results compared favorably with the experimental data and analytical solution.

Pilot-ignited high-pressure direct injection (HPDI) of natural gas in diesel engines results in lower emissions while retaining high thermal efficiency. As a study of HPDI technique, three-dimensional numerical simulations of injection, ignition and combustion were conducted. In particular, the effects on engine combustion of the injection interlace angle between the pilot diesel sprays and natural gas jets were investigated. Numerical simulations revealed ignition and combustion mechanisms in the engine with different injection interlace angles. The results show that altering the interlace angle changes the contact areas between the pilot diesel sprays and the natural gas jets; this affects the heat release rate. Statistical analysis was done to evaluate the expected value and variance of “closeness” between diesel sprays and natural gas jets for different injector tip configurations.

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.