Plenary Speakers
Dr. G. Bruneaux
Institut Français du Pétrole,
Rueil-Malmaison FranceDr. C. Mounaïm-Rousselle
Laboratoire de Mécanique et d'Energétique,
Université d'Orléans, FranceIdeal Sprays for New Generation of Automotive Engines
Abstract
That it is for Compression Ignition or Spark Ignition engines, their improvement related to the economic and environmental constraints implies a control of the following phases: the fuel vaporization and the air-fuel mixture. The objective of this presentation is to make a review about the last decade works concerning the optimisation of the injection process for Internal Combustion engines.
Diesel engines:
The light duty Diesel engine of tomorrow will be faced with two main challenges: to reduce the exhaust emissions at low and mid load, and to increase power at high load while maintaining low smoke emissions. At mid load, one potential solution will be to extend the Low Temperature Combustion mode (LTC, or HCCI) to higher loads. Since this combustion mode is mainly limited by noise issues (also HC , CO at low load), the challenge will therefore consist of better controlling combustion speed in the LTC mode. At high load, increasing power whilst maintaining low smoke emission requires injecting large quantities of fuel in short durations in order to improve combustion efficiency. Such optimised injection strategies may allow for better fuel-air mixing within the combustion chamber. The spray will play a major role for the improvement and optimisation of such low emission combustion systems. The mechanisms of LTC combustion and of Diesel spray air entrainment are presented with the objective of identifying optimised injection strategies addressing the issues related to the extension of LTC towards higher loads and to the improvement of the effective engine power output at high load.
Gasoline Direct Injection (GDI) engines:
The development of GDI engines rests the potential of stratified operation mode, allowing low fuel consumption. The concept is tempting but the classical double challenge remains: increasing the volumetric efficiency and reducing the exhaust emissions. However, the use of direct injection involves the increase of hydrocarbons and smoke emission. Indeed, the hydrocarbons are produced cause of a non-good mixing of the fuel vapour due to the retarding injection and the soot is produced by the wall-wetting. Therefore, the challenge is to provide spray generators sufficiently “flexible” in order to allow ultra lean stratification for a wide range of part-load operating conditions without increase of HC and soot, but also to allow the homogeneous operation mode at higher loads and speeds. All spray characteristics, as spray shape (penetration length and angle), droplet size, velocities distribution and also the concentration difference between liquid and vapour phases are the base of a correct GDI engine operation. The different sprays injectors and strategy will be presented with the objective of identifying optimised injection.
Dr. O.J. Haidn
German Aerospace Center (DLR),
Institute of Space Propulsion
LampoldshausenCryogenic Atomization at Near-Critical Conditions in Liquid Propellant Rocket Engines
O.J. Haidn, J. Lux, M. Oschwald, D. Suslov
German Aerospace Center (DLR), Institute of Space Propulsion Lampoldshausen
Abstract
Quite a large number of liquid propellant rocket engines employ liquid oxygen as oxidizer which is typically injected into the combustion chamber at a temperature below its critical temperature but above its critical pressure. While this specific injection conditions become less important at very high combustion chamber pressures, engines which operate in the pressure range between 4 - 12 MPa are more sensitive to the consequences of the thermodynamic state of the injected fluid.
Following a brief introduction of typical injectors and operating conditions of main stage and upper stage liquid rocket engines such as pressures, temperatures, mass flow rates and pressures and the related non-dimensional numbers typically applied for the characterization of atomization, the paper will focus on the thermodynamic properties of the propellants, especially liquid oxygen, and those of the binary mixtures of oxygen/hydrogen and oxygen/methane a impacts on atomization, mixing and combustion in a liquid propellant rocket engines. Figure 1 shows the hydrogen mole fractionas a function of temperature for the binary systems O2/H2 (left) and O2/CH4 (right). While the first binary mixture shows a large two-phase region which extends to pressures which exceed twice thecritical pressure of oxygen, the two-phase region of the binary mixture of oxygen and methane ceasesto
exist slightly below the critical pressure of oxygen, a fact which may have an impact on the atomizationand mixing behaviour of oxygen when operated in an engine fired with these propellants.
Since almost all thermo-dynamic properties change rather drastically in the vicinity of thecritical point, the paper explores potential influences of these changes onto propellant mixing and combustion. For example, in trans-critical state cryogenic liquids dramatically increase the specificvolume with an almost negligible increase in temperature when heat is added to the fluid, a fact which has an impact on propellant mixing, ignition and flame propagation. Any CFD tool which doesn'taccount for this effect properly will fail to predict the combustion in rocket engines operated under these conditions. Furthermore, the paper will provide recent examples of model rocket combustors operated at near-critical conditions with the propellant combinations LOX/H2 and LOX/CH4 performed at DLR Lampoldshausen.
Dr. Philip Stopford
ANSYS Europe Ltd.
UKThe modelling of liquid sprays in industrial applications using commercial CFD codes
Abstract
Many industrial processes involve the simulation of atomization, droplet break-up, evaporation and wall interaction of liquid sprays. These applications range from spray driers, gas scrubbers and fire suppression to oil combustion in diesel engines, gas turbines and furnaces. This paperreviews the models that are currently used in commercial CFD codes tosimulate common industrial sprays and highlights promising recent developments, as well as issues that require further attention. The talk will be illustrated by examples taken from the author's own experience of industrial consultancy within ANSYS.