FAST EXHAUST CHANNEL OPTICAL-ABSORPTION METHOD AND APPARATUS TO STUDYTHE GAS-EXCHANGE IN LARGE DIESEL-ENGINES

An optical absorption spectroscopic method and apparatus with shorter than 1 ms response time have been used to study the gas exchange proce sses in realistic conditions for a single cylinder of a large diesel e ngine. The method is based on measuring the differential line-of-sight optical uv absorption of the exhaust-gas-contained SO2 as a function of time in the exhaust port area just after the exhaust valves. The op tical absorption by SO2 is determined from Light transmission measurem ents at 280 and 340 nm performed through optical probes installed into the exhaust channel wall. The method has been applied to a continuous ly fired, large, medium speed production-line-type diesel engine with 990 kW rated power. The test engine was operated with standard light f uel oil (MDO Termoshell) and with light fuel oil treated with a sulfur additive {Di-Tert-Butyldisulfid [(CH3)(3)C](2)S-2} The latter was to improve the optical absorption signals without increasing the fouling of the exhaust channel optical probes as in the case of heavier fuel o il qualities. In the reported case of a four-stroke diesel engine meas urement results show that the method can provide time-resolved informa tion of the SO2 density in the exhaust channel and thus give informati on on the single-cylinder gas exchange. During the inlet and exhaust v alve overlap period the moment of fresh air entering into the measurem ent volume can be detected. If independent exhaust gas temperature and pressure data are available, the absorption measurements can readily be used for determining the burnt gas fraction in the exhaust channel. In this work the possibility of using the optical absorption measurem ent to determine the instaneous exhaust gas temperature was studied. B ased on known fuel properties and conventional averaged SO2 measuremen ts from the exhaust channel a known concentration of SO2 was assumed i n the exhaust gas after the exhaust valves opening and before the inle t and exhaust valves overlap period. Together with an exhaust gas pres sure measurement the optical absorption signal was used to determine t he instaneous exhaust gas temperature. Due to the minimal modification s needed by the engine for optical access, and continuously fired oper ation with relevant power levels and realistic fuel qualities, this me asurement method, with some further development, can be useful to obta in time-resolved data from the exhaust channel of real production-line -type diesel engines. (C) 1998 American Institute of Physics.