Contribution to the Catalytic Reduction in Pollutant Emission of Spark-Ignition Engines

Supported by the Federal Office of the Environment, tests aiming at a drastic reduction in pollutants by means of a subsequent exhaust-gas treatment have been carried out at MWM's with a G 234 spark-ignition engine running on natural gas. The tests revealed that the use of three-way catalysts on engines with a cylinder displacement of 1.8 dm³ involves particular requirements to be met by the lambda control system. These could not be fulfilled by altered solutions prevailing on the market in which the air/fuel ratio is oscillating around the catalyst optimum value. Consequently, MWM developed an electronic lambda control system using the voltage of the lambda sensor directly as the controlled variable for the air/fuel ratio of the engine. The maximum conversion rates achieved at constant engine speed of n = 1500 rpm amounted to: NOx = 99% CO = 98% HC = 70%. The objective of further tests is to achieve these results in a reproducible way over the whole performance characteristics of the engine. The endurance run planned under actual operating conditions will demonstrate whether the new lambda control system will stand the test in practical application