Teilprojekt C02 Kubach/Koch

Teilprojekt C02 Kubach/Koch

Spray-Wall-Interaction in the cylinder of a highly charged internal combustion engine with direct injection

Motivation

The simultaneous reduction of fuel consumption and emissions is a challenge for engine developers. Therefore downsized internal combustion engines have been introduced as power units for passenger cars in recent years. These downsized engines are characterized by a smaller combustion chamber while retaining their power output. The engines are charged to compensate for the smaller combustion chamber. Therefore the engines operate at higher loads which results in higher efficiency. Direct injection and high load lead to large quantities of fuel which have to be injected into the combustion chamber. Due to small combustion chambers and the injection of large quantities, the spray-wall-interaction is increased. This interaction produces larger quantities of soot which can form deposits and can lead to self-ignition.

Objectives

In the past only little research has been done on spray-wall-interaction concerning gasoline direct injection engines. Existing research focuses either on general effects or on individual processes. Therefore building a broad knowledge base on how wall interaction affects emission formation and the combustion process under engine conditions is the objective of this project. This includes the investigation of fuel-mixture generation, flow, spray-wall-interaction, pollutant and deposit formation and the retroactive effects on wall interaction using optical measuring systems.

Approach

Experimental Setup

The examination of in-cylinder processes requires optical accessibility of the engine. Two different experimental setups will be used for the experiments.

1. Thermodynamic single-cylinder engine: A thermodynamic single-cylinder engine is not limited to the maximum power output or the maximum engine speed. Therefore the thermodynamic engine differs from other optically accessible engines. The measurements will be performed using endoscopic access.

2. Rapid compression machine: A rapid compression machine will be used for fundamental research due to its excellent optical accessibility. The square combustion chamber is enclosed by plane fused silica windows. These enable distortion-free view onto in-cylinder processes.

To increase reproducibility and to vary boundary conditions coolant temperature, oil temperature and intake air temperature can be conditioned for both test stands.

In order to build a broad knowledge on how wall interaction affects pollutant formation and the combustion process, the relevant parameters have to be measured simultaneously. Optical measurement systems offer simultaneous detection of several variables with high temporal and spatial resolution without any retroactive effects. The flow velocity near the piston is measured in a sub-millimeter scale using Particle Image Velocimetry (PIV) and Laser Doppler Anemometry (LDA). By using a high speed camera in a backlight illumination technique or Mie-scattering methods the spray piston interaction, can be observed. A high speed image intensifier is applied to the test stand to observe the flame-wall-interaction. To measure soot, which is formed during the combustion process, the two-color-method is used. The results serve as means to understand mechanisms as well as an input for generic test stands and modelling.

 Left: Experimental Setup - Rapid compression machine. Right: Coupling of a laser beam into a internal combustion engine.
Left: Experimental Setup – Rapid compression machine. Right: Coupling of a laser beam into a internal combustion engine.