Abstract: An engine control computer estimates NO.sub.x trap temperature based on an estimated midbed temperature of a three-way catalytic converter located upstream from the trap and the effect on NO.sub.x trap temperature of introducing air into the exhaust upstream of the trap during purging of the trap.

Abstract: A flame ionization detector comprises a housing forming a flame chamber for burning a mixture of hydrogen, oxidant and a sample gas. The flame chamber includes: a nozzle in which the sample gas and hydrogen are intimately mixed prior to injection, an igniter for igniting the gas emitted from the nozzle, inlets for hydrogen and oxidant, and an exhaust outlet through which the burnt gases are removed. A collector electrode is electrically insulated from the housing of the flame chamber. The nozzle and flame chamber housing are electrically grounded, and the collector electrode is maintained at a predetermined potential relative to ground. A pre-chamber is disposed adjacent to the flame chamber to provide a substantially constant pressure input of the sample gas to the nozzle.