Uwe Wagner

Investigations of the Formation and Oxidation of Soot Inside a Direct Injection Spark Ignition Engine Using Advanced Laser-Techniques

In this work the formation and oxidation of soot inside a direct injection spark ignition engine at different injection and ignition timing was investigated. In order to get two-dimensional data during the expansion stroke, the RAYLIX-technique was applied in the combustion chamber of an optical accessible single cylinder engine. This technique is based on the quasi-simultaneous detection of Rayleigh-scattering, laser-induced incandescence (LII) and extinction which enables simultaneous measurements of temporally and spatially resolved soot concentrations, mean particle radii and number densities. These investigations show that in our test engine the most important source for soot formation during combustion are pool fires, i.e. liquid fuel burning on the top of the piston. These pool fires were observed under almost all experimental conditions.

Advanced heterogeneous diesel combustion with ultra-low engine emissions and low fuel consumption levels

Increasingly stringent emissions regulations, limited reserves of fossil fuels and CO2-related climate effects have led to the demand for new and diversified engine and vehicle technologies. Compression ignition combustion processes currently offer the highest thermal efficiencies and therefore low specific fuel consumption. Nevertheless, conventional diesel engines face challenges in decreasing NO x and particulate emissions if they are to meet ever more stringent emission regulations. An overview of advanced Diesel technologies and possible ways to address these challenges will be presented in this paper. A recently developed combustion process will be highlighted in detail to demonstrate the emission reduction potential of heterogeneous diesel combustion while maintaining a high thermal efficiency. This combustion process is based on the spatial separation of the different part injections performed during one cycle and offers major advantages in terms of oxygen use, increased exhaust gas recirculation tolerance and significantly lower levels of pollutant formation. This injection strategy is realized by integrating a second injector into the cylinder head of a single cylinder research engine. This second injector is used for the pilot injection and the centrally placed standard injector is used for the main injection. This configuration allows the pilot and main fuels to be injected into different areas of the cylinder. Additionally, the flexible configuration of the proposed injection system allows easy implementation of alternative combustion processes such as homogeneous or partially premixed combustion.

Influence of Operating Parameters on the Thermal Behavior and Energy Balance of an Automotive Diesel Engine

The paper gives a comprehensive overview regarding all relevant operation parameters mainly influencing the energy balance of a state-of-the-art automotive Diesel engine. A detailed experimental analysis of the influence of injection timing and pressure, EGR rate, boost pressure, charge air temperature, coolant temperature and swirl flap position is presented. The investigation includes combustion chamber energy balances based on pressure trace analyses (internal energy balance) as well as outer energy balances that take into account all outgoing and incoming energy flows of the engine based on extensive temperature and flow measurements of the relevant fluids. Measurements of the engine structure temperatures are used to complete the analysis of the thermal engine behaviour depending on the operating parameters. The aim of the paper is to give an overview which operating parameters are crucial for thermal engine application and simulation.

Low Temperature Gasoline Combustion With Diesel Micro-Pilot Injection in a Six-Cylinder Heavy Duty Engine

This paper describes the operation of a heavy duty six-cylinder engine in a dual fuel, Low Temperature Combustion (LTC) mode with very low engine-out NOx und soot emissions according to the US EPA Tier IV final emission limits in the corresponding C1 test cycle. This operation mode makes use of a short pilot injection of diesel fuel, which is injected directly into the cylinder, to ignite a highly diluted, premixed gasoline air mixture. Multicylinder engine operation could be demonstrated over the entire engine operating map with loads of up to 2 MPa BMEP. Expensive aftertreatment systems for NOx and soot emissions are not required.This paper also discusses the challenges involved with the implementation of this combustion system on a multicylinder engine. When transferring the dual fuel LTC from a single cylinder research engine to a multicylinder engine, the design of some engine components, e.g. the camshaft and the piston, were changed. The intake manifold is modified with port fuel injectors for ideal gasoline mixture preparation and equal distribution to all cylinders. To avoid cylinder imbalances, it is possible to control the injected masses of gasoline and diesel fuel for the pilot injection on a per-cylinder basis. Achieving high dilution for ignition delay via EGR and boosted intake pressure to avoid high pressure rise rates and knocking presents challenges for the two-stage turbocharger design. Additionally, high EGR rates and EGR cooling for increased loads are addressed. Finally, experiments to determine the significant control parameters for the combustion process are performed on the engine.In the course of these investigations, dual fuel LTC could be transferred from a single cylinder research engine to a multicylinder engine; previously obtained single-cylinder operating conditions could be achieved even at high loads.Copyright

Controlling Gasoline Low Temperature Combustion by Diesel Micro Pilot Injection

The simultaneous reduction of fuel consumption and pollutant emissions, namely NOx and soot, is the predominant goal in modern engine development. In this context, low temperature combustion concepts are believed to be the most promising approaches to resolve the above mentioned conflict of goals. Disadvantageously these combustion concepts show high peak pressures or high rates of pressure rise due to early ignition and high reaction rates especially at high loads. Furthermore, there are still challenges in controlling combustion phasing. In this context using a small amount of pilot Diesel injected directly into the combustion chamber to ignite a highly diluted gasoline air mixture can overcome the aforementioned difficulties. As the gasoline does not ignite without the Diesel, the pilot injection timing can be used to control combustion phasing. By increasing dilution even high loads with low rates of pressure rise and without knocking are possible. This paper shows the results of experimental investigations carried out on a heavy duty boosted single cylinder Diesel engine. Based on the indicated cylinder pressure, the combustion process is characterised by performing knock analyses as well as thermodynamic analyses. Furthermore an optically accessible engine has been set up to investigate both the Diesel injection and the combustion process by means of digital high speed imaging. Together with the thermodynamic analyses the results of these optical investigations make up the base for the presented theoretical model of this combined Diesel gasoline combustion process. To show the load potential of this Dual-Fuel-CAI concept, the engine was operated at 2100 1/min with an IMEP of 19 bar. NOx emissions did not exceed 0.027 g/kWh.Copyright

An experimental study to assess the potential of homogeneous charge compression ignition diesel combustion with various fuels for light-duty engines

Abstract Single-cylinder engine tests were carried out to assess the potential of homogeneous charge compression ignition (HCCI) diesel combustion compared to the conventional heterogeneous operation mode. For the experiments a single-cylinder engine with a cylinder volume of 0.421 litre was used. Besides the comparison of conventional operation and HCCI operation of the same engine special emphasis was put on the utilization of synthetic fuels such as gas-to-liquid (GtL) or biomass-to-liquid (BtL) fuels. Therefore, in addition to a standard winter diesel, a fuel with mid-sized n-alkanes and mixtures of n-alkanes and aromatic hydrocarbons was used to investigate the influence of different ignitabilities and boiling curves on the combustion. A great advantage of synthetic fuels is the possibility to design them according to the combustion process requirements. In addition, these GtL or BtL fuels will lead to a higher independence from fossil fuels. To assess the potential of HCCI combustion compared to conventional diesel combustion the engine must have the capability to run in both modes. While using the different fuels several engine operation parameters like injection timing and splitting were varied in order to obtain information about their effect on combustion as well as on engine out-emissions. Furthermore, full-load curves for the different fuels were identified to find out where HCCI operation can be applied in an engine map.

Investigation of Soot Concentration and Particle Size Distribution on a Single Cylinder Diesel Engine

The purpose of this study was the characterization of the size distribution and the concentration of the particles emitted by diesel engines under various speed and load points, and different injection pressures. Fine and ultrafine particles emitted by modern diesel engines, in particular those with sizes below 100 nm, are of significant importance for the human health, since the latter are respirable and may have therefore negative effects. The investigations described in this paper provide an insight into the formation of soot particles in the combustion chamber and their number concentration and size distribution in the exhaust gas pipe. The experiments were performed on a single cylinder diesel engine. For the purpose of comparability to multi cylinder engines, the crankshaft drive, the liner, the piston and the cylinder head were based on a heavy duty production engine. The engine was operated with a common rail injection system which was controlled by an electronic control device that offered several degrees of freedom regarding number, duration and timing of the single injections. During the investigations the engine was operated at several speed and load points with and without pilot injection. The in-cylinder soot concentration was measured crank angle resolved with the two-color-method. The F ilter-S moke-N umber (FSN) and the NOx concentration were determined in the exhaust gas. Furthermore the particle number and the particle size distribution were measured by means of a S canning M obility P article S izer (SMPS). The main focus of the experiments was on the investigation of the in-cylinder soot concentration and the particle size distribution running the engine at several injection pressures during different engine speed/load configurations. In order to obtain a potential correlation to common exhaust gas quantification methods, the Filter-Smoke-Number was measured simultaneously. The results of the experiments provide knowledge which is of eminent importance with respect to further diesel combustion development with regard to both the soot concentration and the soot particle properties.Copyright

Vehicle Warm-Up Analysis with Experimental and Co-Simulation Methods

A high accuracy of full-vehicle thermal models are required to predict the vehicle heat-up behaviour at every conceivable combination of driving cycle and ambient air temperature down to −20 °C. Within this work a methodology for modelling the thermal behaviour of an IC-engine is presented. The focus lies on the heat-path beginning with the combustion process followed by heat conduction through the combustion chamber walls and convective heat transfer between engine structure and coolant. The thermal engine model is coupled with other models (HVAC-system, powertrain, etc.) by an independent co-simulation platform in order to describe the virtual vehicle as a whole. Finally, the model validation is performed with two different driving cycles at two different start temperatures. Using the described full-vehicle model the potential of a heat storage system is discussed for several heat-up strategies.

Design and Flow Analysis of a Novel Optically Accessible Heavy Duty Diesel Research Engine

A new single-cylinder optically accessible heavy duty diesel engine has been conceived and constructed at the Institut fur Kolbenmaschinen. Rather than being made from a quartz glass cylinder, the cylinder liner of this engine is modified with three round, flat optical access ports to facilitate laser-optical measurements within the combustion chamber. The flat optical surfaces prove less problematic than a quartz glass cylinder in terms of internal reflections, cleaning procedures, cost, and robustness. A specially adapted piston facilitates the passage of the laser sheet into the piston bowl and provides a view into the bowl at top dead center. Computational fluid dynamics (CFD) simulations were performed in order to estimate the effects of the optically necessary piston and cylinder liner modifications on in-cylinder flow and to compare the flow characteristics with those simulated for a non-modified engine. Emphasis is placed on turbulence behavior before top dead center. The trade-offs and limitations inherent in the modified piston design are discussed in this context. Further optical investigations with this engine will provide insight into the mixture formation and combustion processes. In particular, the soot formation and oxidation processes will be studied under realistic engine operating conditions.Copyright

HCCI Combustion With Various Fuels for Heavy and Light Duty Engines

Single-cylinder engine tests were carried out to assess the influence of several engine operating parameters on HCCI combustion. For the experiments, single-cylinder engines with cylinder volumes of 0.5 and 2 liter were used to represent light and heavy duty application. Engine operation parameters like EGR-rate, air / fuel ratio and injection timing were varied to analyze their influence on the combustion while using different fuels such as Diesel, Gas to Liquid (GtL) and gasoline. Special emphasis was put on synthetic fuels as on the one hand these fuels offer the possibility to “design” them according to the combustion process requirement. On the other hand these GtL — or BtL (Biomass to Liquid) — fuels also lead to a higher independence from fossil fuels. Besides engine out emissions (CO2 , CO, NOx , O2 , HC, soot) and in-cylinder pressure indication for burning process analysis, optical measurement techniques were used for combustion analysis. With different optical probes in-cylinder soot concentration was measured with the Two-Color-Method. In addition UV radiation of OH-radicals was detected with an intensified camera. This procedure allows the differentiation between the beginning of combustion with OH-radical formation and a possible soot formation due to insufficient homogenization.Copyright