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Oxidation of hydrocarbons released from oil layers in internal combustion engines


Lubricating oil present on the piston walls of internal combustion engines contributes to the emission of unburnt hydrocarbons. It is important to understand how these oil layers are released in the piston chamber and how they are burnt.

This project will investigate the oxidation of hydrocarbons desorbed from layers of lubricating oil and crevices in internal combustion engines. Experimental and theoretical studies will be effected to understand/predict the transport and oxidation of hydrocarbons released into the combustion chamber after the completion of the main combustion process.
This project will provide with validated submodels predicting both the adsorption/desorption and oxidation of lubricating oil layers.
The results of the modelling and experiments conducted summarised below, present the basis for further work. Firstly, in the formulation of engine oils which show lower fuel adsorption and desorption and secondly in efficient combustion chamber design, in order to minimise the emission of unburnt hydrocarbons. Based on emission measurements and a knowledge of the pressure and temperature conditions of the exhaust gases during expansion and exhaust strokes, an interpretation of important chemical processes and physical conditions for hydrocardon emission formation were made.

The pressure variation in the constant volume chamber indicated that the oil film temperature is the key parameter in reducing the unburnt hydrocarbon emissions in internal combustion engines caused by fuel desorption from the oil layer. Desorption was reduced when the oil layer was 100(C or more. The theoretical analyses indicate that some fuel is left unburnt after about 10 ms, for example at about 590( of crank angle. Before that time all fuel desorbed from the oil appears to be oxidised.
ITM Aachen will investigate the fundamental processes involved in the adsorption/desorption of hydrocarbons from the oil layers and crevices. Experiments will be carrying out in optically accessible square chamber with variable operating pressure and a homogeneous turbulence field, equipped with a porous metal plate soaked with squalance lubricating oil. Toluene and isooctane will be used as fuels. The influence of cold oil films during engine warm-up time will be simulated by external cooling. A conventional spark ignition system will initiate the combustion, and a pressure transducer will monitor the combustion pressure. The desorption of fuel, and further oxidation by hot combustion products will be monitored by LIF technique and Rayleigh Thermometry. The results will quantity the hydrocarbon emissions from oil films.

Cambridge University (CU) will develop a theoretical model to describe the oxidation of small quantities of hydrocarbons released into the combustion chamber after completion of the main combustion process. Starting with a Monte-Carlo formulation, a more conventional pdf formulation will be developed and compared with the experimental data from ITM and BP.
BP lnternational will provide data of unburned hydrocarbons from a test engine and also numerical estimations of the temperature and pressure distribution in a real test engine. The tests will be carried out in a single-cylinder Ricardo engine which is instrumented so as to be able to predict mean cylinder temperatures during the expansion stroke. The engine will be fitted with small electromagnetic valve, located in the upper cylinder, in order to be able to inject a known quantity of fuel, at low initial momentum, into the post flame gases. Modelling of the flows and main flame combustion for the test engine will be done using the KIVA CFD code with a mass transfer model for the adsorption/desorption of hydrocarbons in the oil layers included. The use of KIVA will allow the prediction of the temperature, pressure and flow distribution in the test engine. This will help CU in the development of the oxidation/transport model.

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BP Oil International Ltd.
EU contribution
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Chertsey road
TW16 7LN Sunbury-on-Thames
United Kingdom

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Participants (2)