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.