| Main Site areas:
Where can you go from here? |
Pressure Analysis
Pressure analysis consists of recording the pressure inside the combustion chamber throughout the combustion cycle. Pressure measurement in the inlet and outlet manifolds and in additional components such as superchargers or turbos are also areas of interest. There are two main types of commonly used pressure sensors.
Pressure measurement in internal combustion engines.
The most common method of recording cylinder
pressure in internal combustion engines is using an electrical
pressure transducer. The electric pressure transducers work by
emitting an electronic signal proportional to the deflection of a
diaphragm when exposed to cylinder pressures.
The piezoelectric transducer is commonly used because of its wide frequency response and linearity over a large range. The piezoelectric transducers are water-cooled to help prevent overheating which causes the quartz elements to break up, deteriorating the performance of the transducer. The transducers need to be located flush with the walls of the cylinder for best results. Flame traps must also be fitted to the pressure transducers to prevent thermal shock, caused by the incursion of fuel or flame. The output of a pressure transducer subjected to thermal shock will generates false readings on the pressure record.
Piezoelectric transducers are also subject to zero drift causing an instability in the pressure reference level. To overcome this several pressure transducers may be used. The particular method described below was developed by R.S.Benson and N.D.Whitehouse [J]:
In the diagram one transducer (HP) is located in the combustion space and the second (LP) is located in the liner approximately mid stroke position. The LP transducer is exposed for part of the stroke to the cylinder pressure and for part of the stroke it is in communication with the crankcase. A third transducer may be fitted in the crankcase. Since this transducer is not subject to zero drift, it can be used to set a baseline for the LP transducer when the later is exposed to the crankcase pressure. The LP transducer is then used to calibrate the baseline for the HP transducer.
The phasing on the pressure diagram is measured using crank angles, these can be measured optically. The signals from the pressure transducer and crankshaft can be converted and transmitted to a computer for processing. The data is usually processed in the form of pressure - crank angle, pressure - volume or heat release - crank angle diagrams. The diagram above shows a typical pressure - crank angle diagram.
Fibre optic pressure sensors
Fibre optic pressure sensors have been developed to measure pressure within a cylinder. A fibre optic pressure sensor consists of single strand of optical fibre connected to an umbilical cable. Any perturbation of the sensor fibre due to pressure effects the amount of light passing through the fibre. Thus the amount of light leaving the fibre may be used to calculate the pressure within a cylinder.
Other types of pressure sensor may be used to measure the pressure in the inlet and exhaust system. Two types commonly used are inductive and strain gauge pressure transducers. The transducers are also water-cooled to reduce the temperature drift and improve durability.
Ref: [1],[4],[8],[J]
| OELWeb Features: |
| Undergraduate course notes can be found
here.
Download FRAN, our fringe analysis software that's free for non-commercial use. Ever heard an opera singer shake the house down? See what they are doing to themselves. Do you know how an internal combustion engine works? Find out here. |