Gerd Grünefeld

Optical investigation of fuel and in-cylinder air-swirl effects in a high-speed direct-injection engine

The primary aim of this study is to investigate current issues of combustion in high-speed direct-injection diesel engines in detail by optical diagnostics. Both fuel and engine design are considered. Recently, measurements of engine-out emissions demonstrated that approximately soot-free combustion can be achieved using a newly designed two-component fuel named BLT. It was composed of 70% butyl levulinate and 30% n-tetradecane (by volume). In this work, the underlying mechanism is clarified by in-cylinder visualization of OH* radicals and soot. In particular, it turns out that in-cylinder soot formation is avoided almost completely, that is, the soot oxidation process is much less important. This is basically achieved by both the oxygen content (about 21%) and the low cetane number (approximately 33) of BLT. The latter leads to enhanced pre-mixing of fuel and air. Consequently, soot formation can be greatly reduced because it depends on the air–fuel ratio of the mixture shortly before high-temperature combustion. The influence of in-cylinder air swirl on combustion and soot formation is also studied for both BLT and conventional diesel fuel, respectively, using the same optical diagnostic. The measurements show that the combustion zone strongly depends on the local gas-flow velocity for diesel fuel. Soot formation decreases with increasing swirl because of enhanced air entrainment and pre-mixing of fuel and air. In addition, the results indicate that soot oxidation is improved under high-swirl conditions for diesel fuel. In contrast, the influence of swirl on the combustion of BLT is overall found to be weak, suggesting that swirl could be reduced in future high-speed direct-injection engines for BLT-like fuels.

Ladungsbewegung und Gemischbildung bei Ottomotoren mit voll variabler Ventilsteuerung

Ein Konzept zur deutlichen Reduzierung des Kraftstoffverbrauchs von Ottomotoren bei gleichzeitiger Darstellung niedrigster Emissionen ist die drosselfreie Laststeuerung mittels voll variabler Ventilsteuerung. Messungen an Mittelklassefahrzeugen zeigen Verbrauchsvorteile von uber 15 % im Vergleich zum Basisfahrzeug mit konventionellem Ventiltrieb bei gleichzeitiger Einhaltung der EU-IV-Emissionsgrenzwerte [1].

Entflammungsverhalten des DI-Ottomotors

Das thermodynamisch beste Konzept fur eine deutliche Reduzierung des Kraftstoffverbrauchs beim Ottomotor ist der Einsatz der Benzindirekteinspritzung. Durch die Direkteinspritzung konnen im Schichtladebetrieb unter anderem Ladungswechsel- und Wandwarmeverluste gesenkt werden. Der in diesem Zusammenhang wichtigste Aspekt ist die Gewahrleistung eines aussetzerfreien Motorbetriebs. Dieser ist nur durch eine sichere Entflammung garantiert. Im vorliegenden Beitrag aus der Tatigkeit der Forschungsvereinigung Verbrennungskraftmaschinen e.V. (FVV) wird untersucht, wie und durch welche Mechanismen ausere Parameter die Entflammungsphase beeinflussen.

Evaluation of partially premixed turbulent flame stability from mixture fraction statistics in a slot burner

Partially premixed combustion is characterized by mixture fraction inhomogeneity upstream of the reaction zone and occurs in many applied combustion systems. The temporal and spatial fluctuations o...

The potential for soot and CO reduction in direct injection diesel engines for passenger cars

As part of the FVV project “The Potential for Soot and CO Reduction for Preventing an Increase in CO Emissions in Direct Injection Diesel Engines with Flexible High-Pressure Direct Injection for Passenger Cars,” a 3-step CO model was created at the Institute for Combustion Engines (VKA) on the basis of extensive kinetic calculations and integrated into the CFD code KIVA and the FVV GPA multi-zone combustion model. To verify the model and as a basis for the CFD simulation, the gas temperature and the concentration of the species CO, O2 and soot were measured during combustion in an optically accessible engine by means of a rapid gas-sampling valve and laser-optical measuring methods. For this purpose, starting from a basic operating point, the start of injection, the rate of exhaust gas recirculation and the rail pressure were varied. The results gained from this test provide an explanation for the soot / CO conflict in diesel engines with advanced injection strategies.

The inflammation behaviour of a DI gasoline engine

From a thermodynamic point of view, the best concept for achieving a substantial reduction in the fuel consumption of gasoline engines is to use direct injection. The application of direct injection in combination with stratified lean operation can, among other things, reduce charge exchange losses and wall heat losses. The most important aspect in this context is to guarantee that the engine operates without misfiring. This can only be ensured by reliable inflammation. The findings presented here are part of the scientific research work of the Forschungsvereinigung Verbrennungskraftmaschinen e.V. (FVV). The aim of the investigations is to analyse how and by which mechanisms external parameters influence the inflammation phase.