Abstract: In a combustion process a fuel is mixed with an oxygen-containing gas in an adjustable ratio. This fuel-gas-mixture is burned and thereby an exhaust gas is produced. At least a part of the exhaust gas is collected and exposed to an ultra violet radiation source, thereby generating positive and negative charge carriers in the exhaust gas by means of a photoelectric charge separation process. The kind or amount of the positive and/or negative charge carriers is detected to produce a measurement value which reflects the amount and/or the charge of the carriers. Therefrom a control signal is derived and the mixture-ratio of the oxygen-containing gas and the fuel, the so-called .lambda.-factor, is adjusted in response to said control signal in order to improve the efficiency of the combustion and to reduce the emission of toxic substances.

Abstract: Aerosol particles, resulting from the combustion of organic substances with insufficient oxygen supply, usually contain toxic, higher hydrocarbonic substances (e.g. tar) on their surface. These substances, e.g. tar, has the property to be photoelectrically more active than other substances contained in the atmosphere. In the method and apparatus according to the invention an aerosol, i.e. the carrier gas containing the particles to be characterized, is used which has been brought to at least one predetermined temperature sufficient for evaporation or decomposition or preventing condensation of molecules on particles of said aerosol that quench or enhance photoelectric activity. Such aerosol is exposed to electromagnetic radiation and, thereby, activated to electron emission. Thereafter the charge of the photoelectrically positively charged particles is determined by means of size selective filter means which are connected to current or charge measuring equipment.

Abstract: The invention relates to a fire detector having a measuring chamber defined by two electrodes, so that a non-ionizing electric field is produced between the electrodes by a DC voltage source. The measuring electrode is connected to the input of a current measuring device without direct connection with the DC voltage source. As soon as charged particles of smoke penetrate into the measuring chamber between the electrodes, the electric field causes the positive and negative particles to drift. The charge drift induces a current into the measuring electrode which is measured.

Abstract: The invention concerns a method and apparatus for electrically charging particles of liquid or solid matter suspended in gases, especially in air. The particle carrying gas is irradiated with ultraviolet light having an energy below the threshold for ionization of the gas, but above the photoelectric threshold of the particles. The actual charging occurs by photoemission of electrons from the particles. The photoelectrons or negative small ions are removed from the neighborhood of the positively charged particles by diffusion to a charge absorbing surface. The photoelectric charging method and apparatus of the present invention are highly effective, particularly for very small particles and yields chemical information on the particles and their surface.

Abstract: The invention concerns a method of producing intense beams of polarized free electrons in which a semiconductor with a spin orbit split valence band and negative electron affinity is used as a photocathode and irradiated with circularly polarized light.