Abstract
Keywords - Mixing, Combustion, Emissions, Engines, Measurement
Abstract - Resolution of the fuel concentration in both time and space is necessary for a correct assessment of the state of mixing of the fuel and air in premixed combustion systems. If the fuel and air are not completely mixed, this can lead to increased production of regulated and non-regulated engine emissions including oxides of nitrogen, carbon monoxide and several unburned hydrocarbons. This paper describes two state-of-the-art high-speed measurement methods for in-cylinder hydrocarbon fuel concentration measurement, resolved in both time and space. These instruments use two different measurement principles for hydrocarbon quantification.
The first of these measurement principles applies Beer's law to the absorption of laser light at a wavelength of 3.392 µm by hydrocarbons. The instrument employing this measurement principle consists of a laser with a high-velocity extractive probe. The velocity of gas in the probe and the residence time of the measurement section are small enough to allow time resolution of approximately 1 ms.
The second of these measurement principles is flame ionisation detection, where hydrocarbon compounds are chemi-ionised, then oxidised in a hydrogen flame. The detector signal is primarily proportional to the mass of supplied hydrocarbons. A model HFR 400 Real Time High Resolution Flame Ionisation Detector employing a high-speed sample gas extraction technique is used for total hydrocarbon analysis The time resolution of the instrument is in the range of 1 ms, as specified by the manufacturer and seen in engine testing. This paper reviews the benefits of the two measurement methods and compares the results of basic in-cylinder experiments using the two instruments.
A discussion of the flow principles and the achievable time resolution of the instruments is given. This includes experimental results identifying the time response of the instruments. Experimental results using the two instruments under non-firing operating conditions are also given. Measurements were taken using the extractive laser instrument in the cylinder and in the intake manifold of a homogeneous charge compression ignition engine, at two operating conditions (corresponding to differing extents of mixing of the fuel and air). Experiments with the real-time high resolution flame ionisation detector consisted of measurements at the spark plug of both a manifold injection and a direct injection spark ignition engine. These results are analysed together with cylinder pressure and crank angle position data that were simultaneously acquired.