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The NO reduction in an ammonia SCR converter has been simulated by a 1D+1D model for a single representative channel to parametrically study the characteristics of the system under typical operating conditions. An appropriate model has been selected interpreting the chemical behavior of the system and the parameters are calibrated based on a comprehensive set of experiments with an Fe-Zeolite washcoated monolith for different feed concentrations, temperatures and flow rates. Physical and chemical properties are determined as well as kinetics and rate parameters and the model has been verified by experimental data at different operating conditions. Three different mechanisms for the surface kinetics to model NO reduction have been assessed and the results have been compared in the cases of steady DeNO performance and transient response of the system. Ammonia inhibition is considered in the model since it has a major effect specifically under transient operating conditions.

Cycle-to-cycle variations in internal combustion engines are known to lead to limitations in engine load and efficiency, as well as increases in emissions. Recent research has led to the identification of the source of cyclic variations of pressure, soot and NO emissions in direct injection common rail diesel engines, when employing a single block injection and operating under long ignition delay conditions. The variations in peak pressure arise from changes in the diffusion combustion rate, caused by randomly occurring in-cylinder pressure fluctuations. These fluctuations result from the excitation of the first radial mode of vibration of the cylinder gases which arises from the rapid premixed combustion after the long ignition delay period. Cycles with high-intensity fluctuations present faster diffusion combustion, resulting in higher cycle peak pressure, as well as higher measured exhaust NO concentrations.

The operation of dual fuel engines, operated with natural gas as main fuel, offers the potential of substantial savings in CO2. Nevertheless, the operating map area where low pollutant emissions are produced is very narrow. Especially at low load, the raw exhaust gas contains high concentrations of unburned methane and, with high pilot fuel portions due to ignition limitations, also soot. The analysis of the combustion in those conditions in particular is not trivial, since multiple combustion modes are present concurrently. The present work focuses on the evaluation of the individual combustion modes of a dual fuel engine, operated with natural gas as main and diesel as pilot fuel, using a combustion model. The combustion has been split in two partwise concurrent combustion phases: the auto-ignition phase and the premixed flame propagation phase.

Measurements of the soot emissions and engine operating parameters from a diesel engine during transient operation were used to investigate the influence of transient operation on the soot emissions, as well as to validate a realtime mean value soot model (MVSM, [1]) for transient operation. To maximize the temporal resolution of the soot emission and engine parameter measurements (in particular EGR), fast instruments were used and their dynamic responses characterized and corrected. During tip-in transients, an increase in the soot emissions was observed due to a short term oxygen deficit compared to steady-state operation. No significant difference was seen between steady-state and transient operation for acceleration transients. When the MVSM was provided with inputs of sufficient temporal resolution, it was capable of reproducing the qualitative and, in part, quantitative soot emission trends.

Numerical simulations of diesel sprays in a constant-volume vessel have been performed with the conditional moment closure (CMC) combustion model for a broad range of conditions. On the oxidizer side these include variations in ambient temperature (800-1100 K), oxygen volume fraction (15-21%) and density (7.3-58.5 kg/m₃) and on the fuel side variation in injector orifice diameter (50-363 μm) and fuel pressure (600-1900 bar); in total 22 conditions. Results are compared to experimental data by means of ignition delay and flame lift-off length (LOL). Good agreement for both quantities is reported for the vast majority of conditions without any changes to model constants: the variations relating to the air side are quantitatively accurately predicted; for the fuel side (viz. orifice diameter and injection pressure) the trends are qualitatively well reproduced.

Emissions and performance parameters of a medium size, medium speed D.I. diesel engine with increased charge air pressure and reduced but fixed inlet valve opening period have been measured and compared to the standard engine. While power output and fuel consumption are slightly improved, nitric oxide emissions can be reduced by up to 20%. The measurements confirm the results of simulations for both performance and emissions, for which a quasidimensional model including detailed chemistry for nitric oxide prediction has been developed.

Numerical simulations of in-cylinder soot evolution in the optically accessible heavy-duty diesel engine of Sandia National Laboratories have been performed with the multidimensional conditional moment closure (CMC) model using a reduced n-heptane chemical mechanism coupled with a two-equation soot model. Simulation results are compared to the high-fidelity experimental data by means of pressure traces, apparent heat release rate (AHRR) and time-resolved in-cylinder soot mass derived from optical soot luminosity and multiple wavelength pyrometry in conjunction with high speed soot cloud imaging. In addition, spatial distributions of soot relevant quantities are given for several operating conditions.

Dual-fuel natural gas engines are seen as an attractive solution for simultaneous reduction of pollutant and CO2 emissions while maintaining high engine thermal efficiency. However, engines of this type exhibit a tradeoff between misfire as well as high UHC emissions for small pilot injection amounts and higher emissions of soot and NOX for operation strategies with higher pilot fuel proportion. The aim of this study was to investigate POMDME as an alternative pilot fuel having the potential to mitigate the emissions tradeoff, enabling smokeless combustion due to high degree of oxygenation, and being less prone to misfire due to its higher cetane number. Furthermore, POMDME can be synthetized carbon neutrally. First, characteristics of POMDME ignition in methane/air mixture and the transition into premixed flame propagation were investigated optically in a rapid compression-expansion machine (RCEM) by employing Schlieren and OH* chemiluminescence imaging.

Oxygenated fuel additives are currently an important research topic for particulate emissions reduction in diesel engines with direct injection (DI) to meet future emission regulations. In this work more than twenty oxygenated hydrocarbons from the literature were considered as diesel fuel additives. Butylal (an acetal compound, chemical formula C9H20O2) offers significant advantages over most other oxygenates in that its physical properties are very close to those of common diesel fuel. Wear scar measurements were conducted to evaluate the lubricity characteristics of diglyme (C6H14O3), ethyldiglyme (C8H18O3), butylal and different diesel-butylal mixtures. The results reveal the low lubricity of all oxygenated compounds. Thus, for the engine tests, a lubricity improver has been added to the diesel-butylal mixtures.

The sooting propensity of dual-fuel combustion with n-dodecane pilot injection in a lean-premixed methane-air charge has been investigated using an optically accessible Rapid Compression-Expansion Machine (RCEM) to achieve engine-relevant pressure and temperature conditions at the start of pilot injection. A Diesel injector with a 100 μm single-hole coaxial nozzle, mounted at the cylinder periphery, has been employed to admit the pilot fuel. The aim of this study was to enhance the fundamental understanding of soot formation and oxidation processes of n-dodecane in the presence of methane in the air charge by parametric variation of methane equivalence ratio, charge temperature, and pilot fuel injection duration. The influence of methane on ignition delay and flame extent of the pilot fuel jet has been determined by simultaneous excited-state hydroxyl radical (OH*) chemiluminescence and Schlieren imaging.

This paper presents numerical simulations of in-cylinder soot evolution in the optically accessible heavy-duty diesel engine of Sandia Laboratories performed with the conditional moment closure (CMC) model employing a reduced n-heptane chemical mechanism coupled with a two-equation soot model. The influence of exhaust gas recirculation (EGR) on in-cylinder processes is studied considering different ambient oxygen volume fractions (8 - 21 percent), while maintaining intake pressure and temperature as well as the injection configuration unchanged. This corresponds to EGR rates between 0 and 65 percent. Simulation results are first compared with experimental data by means of apparent heat release rate (AHRR) and temporally resolved in-cylinder soot mass, where a quantitative comparison is presented. The model was found to fairly well reproduce ignition delays as well as AHRR traces along the EGR variation with a slight underestimation of the diffusion burn portion.

Simulations for a pressure-assisted multi-stream injector designed for urea-dosing in a selective catalytic reduction (SCR) exhaust gas system have been carried out and compared to measurements taken in an optically accessible high-fidelity flow test rig. The experimental data comprises four different combinations of mass flow rate and temperature for the gas stream with unchanged injection parameters for the spray. First, a parametric study is carried out to determine the importance of various spray sub-models, including atomization, spray-wall interaction, buoyancy as well as droplet coalescence. Optimal parameters are determined using experimental data for one reference operating condition.

In the present work numerical simulations were carried out investigating the effect of fuel type, nozzle-geometry variations and back-pressure changes on high-pressure gas injections under application-relevant conditions. Methane, hydrogen and nitrogen with a total pressure of 500 bar served as high-pressure fuels and were injected into air at rest at 200 bar and 100 bar. Different nozzle shapes were simulated and the analysis of the results lead to a recommendation for the most advantageous geometry regarding jet penetration, volumetric growth, mixing enhancement and discharge coefficient. Additionally an artificial inlet boundary conditions was tested for the use with real-gas thermodynamics and was shown to be capable of reducing the simulation time significantly.

A computational study of the near-wall premixed flame propagation in homogeneous charge spark ignited engines is presented on the basis of a spectral concept accounting for flow-chemistry interaction in the flamelet regime. Flame surface enhancement due to wrinkling and modification of the local laminar flame speed due to flame stretch are the main phenomena described by the model. A high pass filter in the turbulent kinetic energy spectrum associated with the distance between the ensemble-averaged flame front location and the solid surface has been also introduced. In addition a probability density function of instantaneous flamelet positions around the above mean flame front location allows to consider statistical effects in a simplified way. Issues of temperature distribution within the boundary layer and associated heat losses, except for the concept of a thermal quenching distance, are thereby not explicitly taken into account.

Combustion engines for decentralized power generation or cogeneration in general, are subject to increasingly stringent pollutant emissions regulations. Motivated by the Europe-;wide lowest allowable NOx levels in Switzerland - particularly in the Zurich metropolitan area with 50 mg/Nm3 at 5% O2 - and in close cooperation with industry, the I.C. Engines and Combustion Laboratory (LVV) of the Swiss Federal Institute of Technology Zurich (ETHZ) has investigated some new operating concepts and engine processes in order to overcome the dilemma between low emissions and high efficiency, which is usually encountered in engine optimization. Our final approach thereby involves the Exhaust Gas Recirculation (EGR) combined with stoichiometric mixture (λ = 1) and a 3-way catalytic converter. The engine is supercharged and the intake mixture aftercooled for high power density and thermal efficiency.

Knock is studied in a single cylinder direct injection spark ignition engine with variable intake temperatures at wide open throttle and stoichiometric premixed ethanol-air mixtures. At different speeds and intake temperatures spark angle sweeps have been performed at non-knocking conditions and varying knock intensities. Heat release rates and two zone temperatures are computed for both the mean and single cycle data. The in-cylinder pressure traces are analyzed during knocking combustion and have led to a definition of knocking conditions both for every single cycle as well as the mean engine cycle of a single operating point. The timing for the onset of knock as a function of degree crank angle and the mass fraction burned is determined using the “knocking” heat release and the pressure oscillations typical for knocking combustion.

State of the art high-pressure fuel injectors offer the ability to inject multiple times per cycle, and can reach very low fuel amounts per injection event. This behaviour allows the application of pilot injections in diesel engine applications or dual fuel engines. In both diesel and dual fuel engines, the amount of pilot fuel affects the engine efficiency. The understanding of the underlying ignition mechanism of the pilot fuel is required to optimize injection parameters and the engines’ fuel consumption. The present work focuses on the differences of ignition mechanisms between long and short injections. The investigation has been performed numerically, using CFD with a well-proven combustion model. The setup used employs a well characterized single orifice injector, injecting into a high temperature, pressurized environment with a composition of 15% oxygen.

The heat release of the low temperature reactions (LTR or cool-flame) under Homogeneous Charge Compression Ignition (HCCI) combustion has been quantified for five candidate fuels in an optically accessible Rapid Compression Expansion Machine (RCEM). Two technical fuels (Naphthas) and three primary reference fuels (PRF), (n-heptane, PRF25 and PRF50) were examined. The Cetane Numbers (CN) of the fuels range from 35 to 56. Variation of the operating parameters has been performed, in regard to initial charge temperature of 383, 408, and 433K, exhaust gas recirculation (EGR) rate of 0%, 25%, and 50%, and equivalence ratio of 0.29, 0.38, 0.4, 0.53, 0.57, and 0.8. Pressure indication measurements, OH-chemiluminescence imaging, and passive spectroscopy were simultaneously implemented. In our previous work, an empirical, three-stage, Arrhenius-type ignition delay model, parameterized on shock tube data, was found to be applicable also in a transient, engine-relevant environment.

In this paper we investigate the effect of the introduction of water in the combustion chamber of a DI-diesel engine on combustion characteristics and pollutant formation, by using water-diesel fuel emulsions with three distinct water amounts (13%, 21% and 30%). For the measurements we use a modern 4-cylinder DI-diesel engine with high-pressure common rail fuel injection and EGR system. The engine investigations are conducted at constant speed in different operating points of the engine map with wide variations of injection setting parameters and EGR rate. The main concern refers to the interpretation of both measured values and relevant thermodynamic variables, which are computed with analytical instruments (heat release rate, ignition delay, reciprocal characteristic mixing time, etc). The analysis of the measured and computed data shows clear trends and detailed evaluations on the behavior of water-diesel fuel emulsions in the engine process are possible.

The addition of hydrogen-rich gas to gasoline in an Internal Combustion Engine seems to be particularly suitable to arrive at a near-zero emission Otto engine, which would be able to easily meet the most stringent regulations. In order to simulate the output of an on-board reformer that partially oxidizes gasoline, providing the hydrogen-rich gas, a bottled gas has been used. Detailed results of our measurements are here shown, such as fuel consumption, engine efficiency, exhaust emissions, analysis of the heat release rates and combustion duration, for both pure gasoline and blends with reformer gas. Additionally simulations have been performed to better understand the engine behaviour and NOx formation.