High-pressure high-temperature cell

1. Introduction

The high-pressure high-temperature cell (HTDZ) at the Paul Scherrer Institute PSI) is a measurement system, in which combustion phenomena, like they are present in an engine can be studied. In the present setup, the HTDZ is used for the investigation of the Diesel engine cycle. The HTDZ provides a facility to study spray combustion in a broad range of parameters which cover and exceed those typically found in a Diesel engine, like:

• chamber temperature: until 550ºC before combustion
• chamber pressure: until 80 bar before combustion
• injection pressure: up to 1500 bar
• multiple injections (injection duration and number): It is possible to inject a number of sprays with different physical properties (delay, duration and ramp) after each other.

In addition to Diesel fuel, also the combustion phenomena of other types of hydrocarbon fuels and diesel additives can be investigated. The HTDZ is optically accessible from all directions and makes it possible to study combustion phenomena during the complete combustion cycle. Therefore, the spray development can be studied from the early beginning of fuel injection until the late stages of the combustion. This is also the big advantage in comparison with an optically accessible engine, in which it is difficult to visualize the combustion phenomena during certain stages of the combustion cycle due to the piston movement. Furthermore, the engine needs lubricants to move the piston more easily, which are not needed in the constant volume combustion chamber. To develop the measurement techniques, also some experiments at flames are being done.

The HTDZ can be operated with an external micro-processor which controls temperature, pressure and timing, providing a facility for suitable attachment of lasers, camera and information about the temperature and pressure evolutionduring the combustion cycle.

2. Aims and related projects

With the HTDZ at the PSI experiments are being performed in order to get a better understanding of the ignition phenomena in a compression ignition engine and spray combustion processes. In particular, validation of the present conceptual model of Diesel combustion (John E. Dec model) is being investigated, including ignition phenomena and soot- and NO_x -formation processes. In addition, the study on the influence of soot- and NO_x development are being performed for oxygenated fuels.

In the next figure the most important phenomena which contribute to an efficient combustion process have been summarised. The red lighted parts are being investigated during the research done at the HTDZ.

The current research projects which are running on the HTDZ are performed in close co-operation with the ETH Zurich and the University of Nijmegen (Netherlands).
The accent of the research is on the following phenomena:

• Development of a reacting and a non reacting spray
• Ignition phenomena of fuels
• Study of soot formation (Laser-induced incandescence, LII)
• Study of NO_x-formation
• Influence of different injection strategies on the combustion process
• Influence of fuel type on Diesel combustion process

3. System setup

In this paragraph a more detailed description of the HTDZ will be given. In the next figure a schematic drawing of the HTDZ is given.

Schematic overview of the high-temperature high-pressure cell

The combustion cell

The combustion chamber volume has a diameter of 110 mm and a depth of 40mm, i.e. a volume of approximated 400cm³ . Optical access orthogonal and parallel to the axis of the cylinder is possible through five windows with a 50mm diameter sealed into the cylinder wall and the cylinder face. The depth of the chamber can be changed using the bottom window of appropriate thickness. Two smaller windows on each side of the injector port provide insight from the top of the cylinder along the spray. In the present configuration, these windows have been unmounted for installation of pressure and temperature sensors.

Gas charge

As there is no piston movement compressed preheated air/nitrogen can be transfered from an electrically heated pressure vessel (autoklav) by a shrouded inlet valve to the cell establishing engine like swirl, pressure and temperature conditions prior to injection. At this moment, measurements are being performed after stabilisation of the air/nitrogen in the system. The gas can be supplied from an external vessel or compressor.

Valves

The cell is provided with a shrouded inlet valve and a fast pressure relief- and safety exhaust valve. The inlet valve is activated by a fast clutch and flywheel assembly which stimulate the conventional camshaft. Cycles can be run at a repetition frequency up to approximately one Hertz.

Injector

A fuel injector is mounted coaxially with the chamber. For the current experiments, a Common Rail Diesel injector manufactured by Ganser Hydromag AG, Neuhausen am Rhein is used. The injector is a solenoid activated needle valve of which the opening can be controlled by a novel fuel injection control unit (Ganser ECU.4.0, BSG GmbH). Temporal evolution of the injection rate can be deliberately adjusted in a broad range (needle-lift signal). It is possible to make a repetition of injections and to inject the fuel in the form of a ramp pulse. The injector is fed with a constant fuel pressure up to 1500 bar provided by an external fuel pump. In addition, the installation of a high-pressure medium ex-changer enables a quick change from one type of fuel to another one.

Heating and cooling system

The autoklav and combustion chamber, inclusive connecting tube can be heated to required temperatures by a set of electric heating elements. An external water cooling system prevents overheating of the pressure sensors, inlet- and exhaust valve and injector. There is a permanent feed-back of the temperature to a micro-processor for safety reasons.

Operating range

The intake gas prior to fuel injection can be prepared up to a pressure of 100 bar at a temperature up to 700K. The construction of the cell allows combustion peak pressures up to 250 bar. The timing of the cycle, i.e. opening of the intake valve, injection time and opening of the exhaust valve are remotely controlable in a wide range. A safety system excludes the choice of non appropriate parameters. The test rig is placed in a containment to prevent any hazard.

4. People

At the PSI, the following persons work together on this project:

• Thomas Dreier
• Thomas Gerber

Last edited May 2005