THE EFFECTS OF NON-AIR MIXTURES ON THE OPERATION OF A DIESEL-ENGINE BY EXPERIMENT AND BY SIMULATION

This paper presents the findings of a detailed investigation to determ ine the performance effects of a diesel engine when the inert nitrogen (N-2) in air is replaced by carbon dioxide (CO2). The requirement for a diesel engine to operate in such a manner is access to free air bei ng prohibited, as is the case with a submarine power generation unit. Numerous projects have investigated non-air-breathing diesel engine sy stems. The more recent ones have concentrated on strategies whereby th e recirculated non-air mixture maintains the thermodynamic properties of free air such that engine performance is not compromised. This has led to the addition of argon and other inert gases. However, systems u tilizing purely fuel, oxygen and carbon dioxide mixtures have not been investigated since the 1960s, and owing to the confidentiality of def ence-related work little public data have been made available. A Perki ns T4.236 truck engine has been configured to operate on a mixture of 70 mol % CO2 and 30 mol % O-2 when preheated to a temperature of 150 d egrees C. Performance results show that under such inlet conditions th e rated brake power of the engine las defined by fuelling rate) degrad es by 20-23 per cent with a subsequent increase in brake specific fuel consumption of 23-28 per cent. In-cylinder observations in relation t o ignition delay and exhaust oxygen concentrations lead to the hypothe sis that the carbon dioxide is seriously affecting both pre-and post-i gnition processes by slowing down reaction rates. Investigations were also carried out to assess the capability of an existing diesel engine model, based on the filling and emptying technique, suitably modified such that it could be used to simulate non-air performance. The modif ications to the model to allow parametric comparisons to be undertaken of non-air brake performance indicators were found to be within 5 per cent of experimental values.