Michael Bargende

Calculating the thermodynamic properties of burnt gas and vapor fuel for user-defined fuels

For real working-process simulations it is essential to know the caloric properties of the working fluid, such as the specific enthalpy and the real gas constant. When using standard-fuels there are established models which describe the caloric variables as functions of temperature, air/fuel-ratio and pressure. In each case, these models were developed for a certain fuel composition and their application to alternative fuels is limited or not valid at all. Thus, an approach is discussed, which is valid for any user-defined fuel.For real working-process simulations it is essential to know the caloric properties of the working fluid, such as the specific enthalpy and the real gas constant. When using standard-fuels there are established models which describe the caloric variables as functions of temperature, air/fuel-ratio and pressure. In each case, these models were developed for a certain fuel composition and their application to alternative fuels is limited or not valid at all. Thus, an approach is discussed, which is valid for any user-defined fuel.

GDI Swirl Injector Spray Simulation:A Combined Phenomenological-CFD Approach

In this work the formation and the evolution of the fuel spray emerging from a hollow-cone swirl injector were investigated. The first aim of the work was to set up a tool for fuel spray simulation in a CFD analysis that can offer a reasonable accuracy with no significant increment in the computational time. The analysis started from a theoretical formulation of the fuel flow inside the injector, based on the potential theory, obtaining an injector model which allows the calculation of the main spray characteristics usually required by the CFD analysis (i.e. droplet velocity, fuel film thickness, droplet size distribution). These parameters can be obtained only from spray cone angle and mass flow rate, which are the data commonly provided by injector manufacturers. Furthermore, a phenomenological approach was also presented, in order to properly simulate in CFD analysis the spray tip penetration in the dense spray zone, without requiring an increase of the spatial grid resolution. Encouraging results were obtained that are in good agreement with the experimental data.

Allgemein gültige Verlustteilung für neue Brennverfahren

Vor dem Hintergrund neuer Brennverfahren wird in diesem Beitrag der Robert Bosch GmbH und des Instituts fur Verbrennungsmotoren und Kraftfahrwesen der Universitat Stuttgart ein neuer Ansatz fur eine detaillierte, allgemein gultige Verlustteilung vorgeschlagen. Ziel ist es, ein einheitliches Werkzeug zur Beurteilung neuer Betriebsstrategien von Otto- und Dieselmotoren und deren Derivate bereit zu stellen.

Besonderheiten der thermodynamischen Analyse von DE-Ottomotoren

In diesem Beitrag, der in Zusammenarbeit der Universitat Stuttgart und DaimlerChrysler entstanden ist, werden Modellansatze zur Brennverlauf- und Arbeitsprozessrechnung bei DE-Ottomotoren im Schichtladebetrieb formuliert und diskutiert. Durch die Kraftstoffeinspritzung wahrend des Kompressionshubes andert sich die im Zylinder befindliche Ladungsmasse in Abhangigkeit des Verdampfungsverlaufes des Kraftstoffs. Dadurch wird die Energiebilanz (innere Energie, Enthalpiestrom des verdampfenden Kraftstoffes und Verdampfungswarme) verandert. All dies beeinflusst die wahrend der Kompression durchzufuhrende Nulllinienbestimmung des gemessenen Druckverlaufs. HC- und CO-Emissionen mussen im Rahmen eines Energiebilanzvergleiches unbedingt berucksichtigt werden. Motorisch gesehen wird deutlich, dass hier noch ein betrachtliches Wirkungsgradoptimierungspotenzial vorhanden ist.

Generally applicate split of losses for new combustion concepts

Against a background of new combustion concepts, a new approach towards establishing a detailed, generally applicable split of losses is proposed in this article by Robert Bosch GmbH und the University of Stuttgart. The aim is to provide a uniform tool for assessing new operating strategies of spark-ignition and diesel engines and their derivatives.

Empirisches Modell zur Vorausberechnung des Brennverlaufes bei Common-Rail-Dieselmotoren

Die Arbeitsprozessrechnung (APR), basierend auf einem Einzonen-Modell und einem vorgegebenen Ersatzbrennverlauf (EBV), stellt weiterhin ein wichtiges Werkzeug in der Motorenentwicklung dar. Die Vorgabe eines den Betriebsbedingungen des Motors entsprechenden EBVs erfolgt typischerweise mit Hilfe eines empirischen Modells. Das hier vorgestellte empirische Modell und der neue EBV gehen optimal auf den in weiten Kennfeldbereichen vorherrschenden Verbrennungstyp des Common-Rail-Motors ein. Wesentliche Neuerung ist somit unter anderem die Berucksichtigung einer Vorverbrennung (VV) und die Abhangigkeit von weitgehend frei wahlbaren Inputgrossen wie dem Raildruck. Basis des neuen Modells war eine ausserst umfangreiche Datenbasis von uber 1800 Betriebspunkten von funf verschiedenen Motoren. Die Arbeiten wurden in der Pkw-Entwicklung von DaimlerChrysler in Stuttgart durchgefuhrt.

Berechnung der thermodynamischen Stoffwerte von Rauchgas und Kraftstoffdampf beliebiger Kraftstoffe

For real working-process simulations it is essential to know the caloric properties of the working fluid, such as the specific enthalpy and the real gas constant. When using standard-fuels there are established models which describe the caloric variables as functions of temperature, air/fuel-ratio and pressure. In each case, these models were developed for a certain fuel composition and their application to alternative fuels is limited or not valid at all. Thus, an approach is discussed, which is valid for any user-defined fuel.For real working-process simulations it is essential to know the caloric properties of the working fluid, such as the specific enthalpy and the real gas constant. When using standard-fuels there are established models which describe the caloric variables as functions of temperature, air/fuel-ratio and pressure. In each case, these models were developed for a certain fuel composition and their application to alternative fuels is limited or not valid at all. Thus, an approach is discussed, which is valid for any user-defined fuel.

Transient simulation with scavenging in the turbo spark-ignition engine

A promising approach to decrease fuel consumption in spark-ignition engines involves supercharging with an exhaust-gas turbocharger, by way of which load point shifting and/or longer transmission ratios can be shown. Direct injection provides additional benefits, when combined with exhaust-gas turbocharging and the use of devices for manipulating the phasing of inlet and exhaust control times. On account of the many degrees of freedom this mode of operation offers, the use of computational simulations to design the gas exchange is extremely advantageous, to reduce both time and expense during development. To this end, the effects of scavenging in a turbo SI engine at full load were thoroughly examined at the Institute for Internal Combustion Engines and Automotive Engineering (IVK) with the aid of a comprehensive development toolkit.

Das Zylindermodul Neue Simulation nicht nur für zukünftige Brennverfahren

Unbestritten spielt die Simulation der innermotorischen Vorgange bei der Optimierung von Wirkungsgrad und Emissionen des Gesamtfahrzeugs eine entscheidende Rolle. Dabei werden die Anforderungen an die Simulation immer groser — sowohl bezuglich der Genauigkeit als auch durch neue Brennverfahren und durch den Einsatz alternativer Kraftstoffe. Hierbei durfen Verbrennung und Brennraum nicht mehr isoliert vom Gesamtsystem betrachtet werden. Gerade bei der Optimierung instationarer Vorgange ist die nahtlose Einbindung der Simulation des „Zylinders“ in die Ladungswechsel-Simulation und letztlich in die Abbildung des gesamten Fahrzeugs von entscheidender Bedeutung. Im Rahmen des FVV-Forschungsvorhabens Nr. 869 entwickelt das IVK der Universitat Stuttgart ein Simulationswerkzeug fur die Gesamtprozessanalyse.

Prediction of burn rate, knocking and cycle-to-cycle variations of binary compressed natural gas substitutes in consideration of reaction kinetics influences:

Since zero-dimensional/one-dimensional simulations of natural gas spark-ignition engines use model theories similar to gasoline engines, the impact of changing fuel characteristics needs to be taken into consideration in order to obtain results of higher quality. For this goal, this article proposes some approaches that consider the influence of binary fuel mixtures such as methane with up to 40 mol% of ethane, propane, n-butane or hydrogen on laminar flame speed and knock behavior. To quantify these influences, reaction kinetics calculations are carried out in a wide range of the engine operation conditions. Obtained results are used to update and extend existing sub-models. The model quality is validated by comparing simulation results with measured heat release rates and knock limit. The benefit of the new sub-models is demonstrated by predicting the influence the fuel takes on engine operating limits in terms of knocking and lean misfire limits, the latter being determined using a cycle-to-cycle variation model.