Diesel NoX Control

Abstract

NOx emissions of mass-produced Diesel-powered passenger cars in the inertia weight class of 910 to 1360 kgs range between 1.1 and 1.5 g/mile (FTP). A reduction can be effected in various ways, the most important being exhaust gas recirculation (maximum reduction by a factor of 1.5) and drivetrain modifications (maximum reduction 20 %). EGR, however, is problematic not only because of component durability and driveability but also because of the mixture ratios which may be required (0 % with the engine cold, as much as 60 % at idle, and less than 5 % at WOT). The EGR rate should be in a set and carefully controlled relationship to the amount of fuel injected, and distribution to the cylinders should be even. The paper discusses the effect of EGR on fuel consumption and the emission of HC, CO, NOx, particulates, and smoke under steady-state operating conditions; as well as the distribution of recirculated exhaust gas to the cylinders of a 37 kW 1.5 1 VW Diesel engine. The fuel economy and the emission of HC, CO, and NOx of prototype vehicles weighing between 910 and 1360 kgs and equipped with naturally-aspirated or turbocharged Diesel engines with or without EGR were measured, indicating that 1. Emissions of 1 g/mile (FTP) are possible in prototypes weighing 910 kgs or less. 2. A well-controlled EGR system is required to ensure 1 g/mile in heavier cars. 3. Even a combination of all known methods, EGR, drivetrains for low engine speeds, and injection timing, cannot reduce the emission of NOx to 0.4 gpm.