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Technical Paper

Reduction of NOx Emissions of D. I. Diesel Engines by Application of the Miller-System: An Experimental and Numerical Investigation

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.
Technical Paper

Combustion Features and Emissions of a DI-Diesel Engine with Air Path Optimization and Common Rail Fuel Injection

Emission and performance parameters of a medium size, and medium speed D.I. diesel engine equipped with a Miller System, a new developed High Pressure Exhaust Gas Recirculation System (HPEGR), a Common Rail (CR) system and a Turbocharger with Variable Turbine Geometry (VTG) have been measured and compared to the standard engine. While power output, fuel consumption, soot and other emissions are kept constant, nitric oxide emissions could be reduced by 30 to 50% depending on load and for the optimal combination of methods. Heat release rate analysis provides the reasons for the optimised engine behaviour in terms of soot and NOx emissions: The variable Nozzle Turbocharger helps deliver more oxygen to the combustion process (less soot) and lower the peak gas temperature (less NOx).
Technical Paper

Near-Wall Unsteady Premixed Flame Propagation in S.I. Engines

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.
Technical Paper

A Computational Investigation of Unsteady Heat Flux Through an I.C. Engine Wall Including Soot Layer Dynamics

This paper deals with the influence of a wall soot layer of varying thickness on the unsteady heat transfer between the fluid and the engine cylinder wall during a full cycle of a four-stroke Diesel engine operation. For that purpose a computational investigation has been carried out, using a one-dimensional model of a multi-layer solid wall for simulating the transient response within the confinement of the combustion chamber. The soot layer is thereby of varying thickness over time, depending on the relative rates of deposition and oxidation. Deposition is accounted for due to a thermophoretic mechanism, while oxidation is described by means of an Arrhenius type expression. Results of the computations obtained so far show that the substrate wall temperature has a significant effect on the soot layer dynamics and thus on the wall heat flux to the combustion chamber wall.
Technical Paper

Numerical Investigation of Nozzle-Geometry Variations and Back-Pressure Changes on High Pressure Gas Injections under Application-Relevant Conditions

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.
Technical Paper

Development and Validation of a Phenomenological Mean Value Soot Model for Common-Rail Diesel Engines

A mean value soot model (MVSM) was developed and validated for the realtime prediction of the raw, engine-out soot emissions from common rail diesel engines. Through the consideration of five representative states during the combustion cycle, the developed MVSM determines the engine out soot emissions based on the soot formation and oxidation processes, using only parameters available from a standard engine control unit. 16 model parameters are used to describe the engine, fuel, and combustion characteristics, and must be determined for each engine and fuel combination. The MVSM was parameterized and validated using the measured soot emissions from two different engines operating with a total of three different fuels. After parameterization, the MVSM was capable of qualitatively and quantitatively reproducing the soot emissions for operating points throughout the entire operating map, including for operating regimes not considered during the parameterization.
Technical Paper

Experimental Validation of a Global Reaction Model for a Range of Gasolines and Kerosenes under HCCI Conditions

Compact and computationally efficient reaction models capable of accurately predicting ignition delay and heat release rates are a prerequisite for the development of strategies to control and optimize HCCI engines. In particular for full boiling range fuels exhibiting two-stage ignition a tremendous demand exists in the engine development community. To this end, in a previous investigation, a global reaction mechanism was developed and fitted to data from shock tube experiments for n-heptane and five full boiling range fuels. By means of a genetic algorithm, for each of these fuels, a set of reaction rate parameters (consisting of pre-exponential factors, activation energies and concentration exponents) has been defined, without any change to the model form.
Technical Paper

Integration of a Cool-Flame Heat Release Rate Model into a 3-Stage Ignition Model for HCCI Applications and Different Fuels

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.
Technical Paper

THE Post Injection: Coalescence of 3D CFD-CMC Simulation, 2D Visualizations in a Constant Volume Chamber and Application in a Modern Passenger Car Diesel Engine

Past research has shown that post injections have the potential to reduce Diesel engine exhaust PM concentration without any significant influence in NOx emissions. However, an accurate, widely applicable rule of how to parameterize a post injection such that it provides a maximum reduction of PM emissions does not exist. Moreover, the underlying mechanisms are not thoroughly understood. In past research, the underlying mechanisms have been investigated in engine experiments, in constant volume chambers and also using detailed 3D CFD-CMC simulations. It has been observed that soot reduction due to a post injection is mainly due to two reasons: increased turbulence from the post injection during soot oxidation and lower soot formation due to lower amount of fuel in the main combustion at similar load conditions. Those studies do not show a significant temperature rise caused by the post injection.
Technical Paper

Optical Investigations of Soot Reduction Mechanisms using Post-Injections in a Cylindrical Constant Volume Chamber (CCVC)

Past research has shown that post injections have the potential to reduce Diesel engine exhaust PM concentration without any significant influence in the NOx emissions. In earlier research it was observed that soot reduction due to a post injection is based on three reasons: increased turbulence (1) and heat (2) from the post injection during soot oxidation and lower soot formation due to smaller main injection for similar load conditions (3). The second effect of heat addition during the soot oxidation is debated in the literature. The experimental investigation presented in the current work provides insight into the underlying mechanisms of soot formation and reduction using post injections under different operating conditions. The experimental data have been obtained using a cylindrical constant volume chamber with high optical access. The soot evolution has been obtained using 2-color-pyrometry.
Technical Paper

Experimental Investigation on the Gas Jet Behavior for a Hollow Cone Piezoelectric Injector

Direct injection of natural gas in engines is considered a promising approach toward reducing engine out emissions and fuel consumption. As a consequence, new gas injection strategies have to be developed for easing direct injection of natural gas and its mixing processes with the surrounding air. In this study, the behavior of a hollow cone gas jet generated by a piezoelectric injector was experimentally investigated by means of tracer-based planar laser-induced fluorescence (PLIF). Pressurized acetone-doped nitrogen was injected in a constant pressure and temperature measurement chamber with optical access. The jet was imaged at different timings after start of injection and its time evolution was analyzed as a function of injection pressure and needle lift.
Technical Paper

Simulations of In-Cylinder Processes in a Diesel Engine Operated with Post-Injections Using an Extended CMC Model

In this study, numerical simulations of in-cylinder processes associated to fuel post-injection in a diesel engine operated at Low Temperature Combustion (LTC) have been performed. An extended Conditional Moment Closure (CMC) model capable of accounting for an arbitrary number of subsequent injections has been employed: instead of a three-feed system, the problem has been described as a sequential two-feed system, using the total mixture fraction as the conditioning scalar. A reduced n-heptane chemical mechanism coupled with a two-equation soot model is employed. Numerical results have been validated with measurements from the optically accessible heavy-duty diesel engine installed at Sandia National Laboratories by comparing apparent heat release rate (AHRR) and in-cylinder soot mass evolutions for three different start of main injection, and a wide range of post injection dwell times.
Technical Paper

Numerical Investigation of Soot Dynamics at Engine-Relevant Conditions

Formation of soot in an auto-igniting n-dodecane spray under diesel engine relevant conditions has been investigated numerically. As opposed to research addressing turbulence-chemistry interaction (TCI) by coupling diffusive turbulence models with more sophisticated models in the context of Reynolds-Averaged Navier-Stokes equations (RANS), this study employs the advanced sub-grid scale k-equation model in the framework of a Large Eddy Simulation (LES) together with the uninvolved Direct Integration (DI) approach. A reduced n-heptane chemical mechanism has been employed and artificially accelerated in order to predict the ignition for n-dodecane accurately. Soot processes have been modelled with an extended version of the semi-empirical, two-equation model of Leung, which considers C2H2 as the soot precursor and accounts for particle inception, surface growth by C2H2 addition, oxidation by O2, oxidation by OH and particle coagulation.
Technical Paper

Analysis of Factors Influencing Particulate Matter Emissions of a Compression-Ignition Direct-Injection Engine

The relative amounts of heat released by premixed and by diffusion controlled combustion is varied in a compression-ignition engine run on the test bench through variation of four operating parameters. Exhaust gas is led to a differential mobility particle sizer and to filters that are loaded for gravimetric analysis. Particle size distributions are acquired in the 16÷630 nm range of electrical mobility diameters. Opacity readings of the exhaust gas are taken, cylinder pressure is indicated, a value for the combustion noise is computed; gaseous emissions are recorded and heat release rates based on cylinder pressure analysis are evaluated. Two full factorial experiments at 2 bar bmep 2000 rpm are run as 24 combinations of four factors: Injection pressure 400 and 1200 bar, with and without pilot injection, 1/3 and 1/4 mass-fraction exhaust gas recirculation, late, middle and early start of injection.
Technical Paper

Oxygenated Fuels for Particulate Emissions Reduction in Heavy-Duty DI-Diesel Engines with Common-Rail Fuel Injection

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.
Technical Paper

Natural Gas Engines for Cogeneration: Highest Efficiency and Near-Zero-Emissions through Turbocharging, EGR and 3-Way Catalytic Converter

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.
Technical Paper

Influence of Water-Diesel Fuel Emulsions and EGR on Combustion and Exhaust Emissions of Heavy Duty DI-Diesel Engines equipped with Common-Rail Injection System

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.
Technical Paper

Clean Engine Vehicle A Natural Gas Driven Euro-4/SULEV with 30% Reduced CO2-Emissions

The goal of the Clean Engine Vehicle project (CEV) was the conversion of a gasoline engine to dedicated natural gas operation in order to achieve a significant reduction in CO2 emissions. The targeted reduction was 30% compared with a gasoline vehicle with similar performance. Along with the reduction in emissions, the second major requirement of the project, however, was compliance of the results with Euro-4 and SULEV emission limits. The project entailed modifications to the engine and the pre-existing model-based engine control system, the introduction of an enhanced catalytic converter and downsizing and turbocharging of the engine. As required by the initiators of the project, all components used were commonly available, some of them just being optimized or modified for natural gas operation.
Technical Paper

Influence of Hydrogen-Rich-Gas Addition on Combustion, Pollutant Formation and Efficiency of an IC-SI Engine

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.
Technical Paper

Influence of EGR on Combustion and Exhaust Emissions of Heavy Duty DI-Diesel Engines Equipped with Common-Rail Injection Systems

At the Internal Combustion Engines and Combustion Laboratory of the Swiss Federal Institute of Technology in Zurich we are currently developing low emission strategies for heavy duty diesel engines that engine manufacturers can implement to meet stringent emissions regulations. The technologies being studied include high-pressure fuel injection (with common-rail injection system), multiple injection strategies (with pilot or post injections), turbo charging, exhaust gas recirculation (cooled EGR), oxygenated fuels and the optimization of the air management system. This paper focuses on the effects of exhaust gas recirculation (cooled EGR) in combination with very high injection pressure. Measurements were carried out on a heavy-duty diesel single-cylinder research engine equipped with a modern common rail fuel injection. The engine investigations were conducted in different operating points in the engine map covering wide speed and load ranges.