Roland Baar

Study on Combustion Process and Emissions of a Single-Cylinder Diesel Engine Fueled with DMC/Diesel Blend

AbstractDimethyl carbonate (DMC) has advantages of solubility in diesel and high oxygen content. Its application in diesel engines has won increasing popular focus. A DMC/diesel blend with 10% DMC by volume (D10) is prepared to investigate its combustion process and emissions. Although the volumetric energy density drops slightly with the addition of DMC, minor adjustments of the injection parameters would achieve the output power of the original engine. The heat release process is more concentrated because the addition of low boiling point DMC boosts the atomization and mixing with air of the blended fuel. Hence the indicated thermal efficiency of D10 increases remarkably as compared with reference diesel. The emissions of hydrocarbons and carbon monoxide are apparently reduced for D10. Nitrogen oxide (NOx) emissions increase owing to the addition of oxygenated fuel DMC, but this is reduced by the decline in engine load. The oxygen from the D10 blend plays a role in reducing particulate matter (PM) emiss...

Combustion Cycle-by-Cycle Variations in a Common Rail Direct Injection Engine Fueled with Dimethyl Carbonate–Diesel Blend

AbstractIn consideration of the multiple split injection, heavy exhaust gas recirculation (EGR) atmosphere, high latent heat of vaporization of dimethyl carbonate (DMC), and low cetane number, the combustion variations of both diesel and D10 (a fuel blend of 10% of DMC in diesel) have been investigated with characteristic parameters of indicated mean effective pressure pmi, peak pressure pmax, and initial 10% combustion duration θd. Results show that the cyclical coefficients of variation (COVs) of three characteristic parameters are lower than 2%. This means good combustion quality thanks to the precise control of fuel injection. The COVs for diesel are much smaller than those for D10 fuel. The COVs of pmi, pmax, and θd rise with a declining center of heat release (COHR), while the COVs show visible growth with the increase in EGR rate. The anticipation of possible combustion instability due to pilot injections did not happen. Both pmax and θd have good corresponding relations with pmi. The pmi positivel...

Bidirectional flow measurement based on the differential pressure method for surge analysis on a small centrifugal compressor

To obtain a high temporal resolution of mass flow data, a flowmeter based on the differential pressure method has been developed. It is capable of detecting negative flow for investigations of dynamic effects in small centrifugal compressors used for turbocharging automotive internal combustion engines. Experiments were performed at a hot gas test bench focusing on the surge characteristics at different turbocharger speeds and the influence of volume modifications downstream of the compressor. Instantaneous operating points could be traced in the compressor map including the typical orbits at deep surge resulting from the cyclic character of the phenomenon.

Combustion features under different center of heat release of a diesel engine using dimethyl carbonate/diesel blend

ABSTRACT Experiments were performed in a single cylinder common-rail diesel engine that adopts a low temperature premixed charge compression ignition (PCCI) mode. Combustion features of dimethyl carbonate (DMC)-diesel blends under various centers of heat release (COHRs) were revealed in details. With retarding of COHR, all the peaks of pressure and pressure rise rate and bulk gas temperature are postponed and declined in sequence. Normally, the crank angle of peak pressure is quite close to the COHR, while the peak of bulk gas temperature appears about 7°CA after COHR as a rule. The prolongation can be demonstrated at every stage of combustion such as q10 and q90 with the COHR being put backward. In addition, the heat release of diesel is completely slower than that of D10 fuel at various stages. Unfortunately, retarding of COHR implies a declining thermal efficiency of engines as well as a higher cyclic variation in general. Nevertheless, D10 blend has higher thermal efficiency than diesel thanks to high oxygen content of DMC and low boiling point that prompts better fuel atomization and complete combustion. Meanwhile, the cyclical variation of D10 is greater than diesel fuel owing to the low heat value, high latent heat of vaporization, and poor flammability of DMC. As a total, a comprehensive understanding of PCCI combustion features under different COHRs can be conducive to conducting effective management of combustion process and manipulating the subsequent emission performance to a favorable level.

Effects of new nozzle hole configurations on air utilization and soot emissions of diesel engines

With conventional combustion processes there remain unused regions with air between the injection jets. To utilize these a 14-hole nozzle and a nozzle with 6 smaller and 6 larger spray hole diameters were developed. Both nozzles show strongly increased soot emissions. The optical analyses reveal improved air utilization during the main injection which leads to higher local combustion temperatures for both. The higher temperatures support the soot formation. In the later stages of the combustion the new nozzles show poorer air utilization than the references. The reference nozzles show a distinct backflow of the combustion from the piston bowl which improves the air utilization and support the soot oxidation. With the new nozzles this is less developed because of a lower spray momentum due to the smaller spray hole diameters.

Ein neues Verfahren zur Bedatung von aerodynamischen, thermischen und mechanischen Turboladermodellen

Turbolader fur Verbrennungsmotoren werden heute typischerweise an speziellen Turbolader- Prufstanden vermessen. Die Ergebnisse dienen dazu, die Turbolader grundsatzlich zu bewerten, verschiedene Hersteller oder Baustande miteinander zu vergleichen und Daten fur die Motorprozessrechnung zu liefern. Die Vorschrift zur Vermessung ist in SAE J922 beschrieben. Es hat sich in den letzten Jahren herausgestellt, dass die Vorschrift aufgrund zunehmender Anforderungen heute nicht mehr ausreichend ist. Es geht dabei insbesondere um den Einflusse der Warmeubergange, die einerseits die Bewertung der Aerodynamik beeinflussen und andererseits fur moderne Antriebsstrangsimulationen eine notwendige Information als eigenes Modell darstellen. Daher wird vielfach nach einer Erweiterung der Untersuchungsmoglichkeiten gesucht. Insbesondere die Stromungssimulation (CFD) hat sich, vor allem in Kombination mit der Warmeubergangssimulation (CHT), als gute Moglichkeit erwiesen, fehlende Daten bereit zu stellen. Der zentrale Nachteil dabei ist jedoch, dass solche Simulationen einerseits sehr zeitaufwendig sind und andererseits CAD-Daten voraussetzen, die selten vorliegen. An der TU Berlin wird daher seit einigen Jahren an einem neuen Messverfahren gearbeitet, das die bestehende Messvorschrift mit vertretbarem Aufwand erweitert. Es hat sich dabei als notwendig erwiesen, neue Methoden zur Bestimmung der Turbinenaustrittstemperatur und des isentropen Turbinenwirkungsgrads. Auserdem sind neue Verfahren zur Definition eines adiabaten und damit nahezu warmeubergangsfreien Zustands sowie neue Verfahren zur Extrahierung und Modellierung von Warmeubergangen in Turboladern zu entwickeln. Dieser Beitrag fasst den aktuellen Stand dazu an der TU Berlin zusammen.

High-level phlegmatization of an ICE for the use in a series hybrid powertrain

The electrification of power trains offers high potential for fuel savings. Furthermore, the use of a series hybrid technology allows simplifying the internal combustion engine due to fewer requirements concerning dynamics, power, and torque – it is possible to phegmatize the internal combustion engine. In this project a simulation model of a series hybrid is presented where an internal combustion engine is only working as a generator. The basic engine is a 4-cylinder direct injecting turbocharged spark-plug engine. Variable valve-timing as well as throttle and wastegate control are removed. The internal combustion engine is only working at its optimum point. Phenomenological thermal models of the engine and the transmission are presented. Furthermore, thermal models of the electrical components were developed. A thermal management system is shown as well as a hybrid operating strategy. The power train model is calculated in the WLTC and fuel savings are investigated.

Turbocharger Heat Transfer Determination with a Power Based Phenomenological Approach and a CHT Validation

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Turbocharger Heat Transfer Determination with a Power Based Phenomenological Approach and a CHT Validation Bojan Savic, Xunan Gao, Roland Baar

Determination of the isentropic turbine efficiency due to adiabatic measurements and the validation of the conditions via a new criterion

The determination of the isentropic turbine efficiency under adiabatic and SAE boundary conditions is studied in this paper. The study is structured into two parts. The first part describes the possibility of measuring the isentropic turbine efficiency directly. Normally this is not possible in measurements conducted following the SAE J922 guidelines. Therefore, the experiments have been carried out under adiabatic conditions, and combined with improved measuring equipment. The results were compared with adiabatic computational fluid dynamics simulations of this turbocharger. In the second part, a new criterion is defined in order to evaluate the quality of the adiabatic measurements and compare them with standard measurements. The investigation has been carried out with multiple turbochargers ranging from very small to medium passenger car size turbochargers. In the end, a possible application for the criterion is given.

Einfluss der Kraftstofftemperatur auf die Strahlausbreitung im Dieselbrennverfahren

Die Reduzierung von Emissionsgrenzwerten, wie der EU6 Norm, stellen die Brennverfahrensentwicklung vor stetig wachsende Herausforderung. Zur Erreichung der gesetzlich gesteckten Ziele ist ein Zusammenspiel von Abgasnachbehandlungssystemen und der innermotorischen Emissionsabsenkung zwingend notwendig. Besonders im Hinblick auf den Mehraufwand durch Komponenten der Abgasnachbehandlung ist eine Optimierung des Brennverfahrens zielfuhrend, durch welche im besten Fall der Verbrauch bei sinkenden Rohemissionen konstant gehalten werden kann.