An alarming number of compression ignition (CI) engines in the transport, mining and heavy engineering environments have been failing due to combustion irregularities within their combustion chambers. It has been found that diesel fuels containing contaminants or diesel fuels with poor lubricity characteristics lead to stickiness of diesel injector needles, which badly affects injector spray patterns resulting in the phenomenon of “cold combustion”. This study has been undertaken to develop a technique for detecting and preventing the damage resulting from this deviation in the combustion of a diesel engine. The technique has been formulated with a view to being as non intrusive as possible, so as not to require major modification of an existing test engine to accommodate the technique. The practice of monitoring individual cylinder exhaust gas temperatures (EGTs) proved to be an effective way of determining whether potentially destructive combustion abnormalities were taking place within the diesel engine. By recording these temperatures at certain stages during the engine’s operation, taking their average, and comparing each one to this average it is also possible to isolate the location of the combustion abnormality. This method proved to be most effective at full loads and maximum fuel delivery where combustion temperatures are highest and the effects of poor combustion are most noticeable and potentially damaging. The second goal was to develop a small, portable electronic device that makes use of the monitoring technique developed and provides a visual and audible alarm to notify a vehicle operator or technician of a combustion fault within a diesel engine. A Combustion Monitoring System (CMS) prototype was developed and tested on a small naturally aspirated engine at the University of Pretoria’s engine testing facilities. The prototype met its primary goal of detecting simulated combustion abnormalities under a variety of test conditions. It is envisaged that the monitoring techniques applied in developing the CMS unit may eventually be incorporated into the powerful processing abilities of the modern diesel Engine Control Unit (ECU). In its current form the CMS prototype is a useful tool in sensing combustion related malfunctions within a diesel engine and preventing damage from occurring.
Dissertation (MEng)--University of Pretoria, 2009.