Abstract
The dynamic monitoring of oil consumption in IC engines is approached with various techniques ranging from radioactive counting to detection of halogenated tracer compounds or polyaromatic hydrocarbon tracers, to monitoring unburned hydrocarbons as residues from engine oil. This article discusses the method of gaseous SO2 measurement in raw exhaust its benefits and limitations of todays status. Modern engines consume about 2 to 5 g/h of engine oil under low and medium load but consumption may go up to 130 g/h in negative load conditions. Particulate filters must be desulfated every 5000 km even when sulfur free fuel is in use. For the oil measurement in the raw exhaust all possible Sulfur compounds are converted to SO2 in a hot oxidizing atmosphere. Additional pure oxygen in the form of ozone is added to the oxidizer for very low lambda engine conditions and the conversion of sulfur on particulates into SO2. A sensitive mass spectrometer operating in an ion molecule ionization mode measures gaseous SO2 from concentrations of 0.02 ppm to 50 ppm in measurement cycles from 2 Hz to 0.2 Hz depending on if long term measurement or dynamic operation is chosen. Technical description of pressure reduction, gas transfer, oxidation efficiencies and lower detection levels of the instrumentation are given as well as data on a complete engine map and data on reproducibility of the SO2 method are presented.
Highlights
Downsizing of engines in cylinders and capacity, increasing compression ratios and MEPs, turbocharging, reduction of piston friction, use of CNG as modern fuel: all these strategies result in elevated temperatures of engine parts and engine oil, reduced oil viscosity, elevated blow by rates, and increasing oil loss of modern IC engines
For engine operating conditions below lambda 1 where the residual oxygen concentration in the raw exhaust goes to zero, additional oxygen must be added to the oxidizing chamber
At higher sulfur levels there will be a higher offset in the SO2 signal and the resolution of SO2 measurement related to engine oil is diminished
Summary
Downsizing of engines in cylinders and capacity, increasing compression ratios and MEPs, turbocharging, reduction of piston friction, use of CNG as modern fuel: all these strategies result in elevated temperatures of engine parts and engine oil, reduced oil viscosity, elevated blow by rates, and increasing oil loss of modern IC engines. Desulfation is typically achieved by injection of fuel or as post injection, the amount of hydrocarbons must be chosen in a way that only SO2 desorption takes place and not reduction of sulfur into H2S This would cause a severe odor problem and extensive testing is necessary. The survival of tracers at high combustion temperatures may be tackled with inorganic halogenated compounds but halogenated compounds may form aggressive acids that are not welcome by engine operators Another approach is the addition of aromatic compound like pyrene that have very high flame resistance and have high boiling points and will condensate at low oil temperatures and low engine load applications. Chamber is in both liquid and vapor form, a consistent sulfur concentration in the oil is required in order to assume that consumed oil in the exhaust that has the same concentration of sulfur as in the original oil
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