:Diesel engine particulate certification, heretofore limited to on-highway truck engines, will be expanded in scope beginning in 1996 to eventually include all diesel engines. Legislation in Europe, Japan and California will extend certification efforts to engines powering generator sets, construction/agricultural vehicles, locomotive and marine engines, using “steady-state” test guidelines proposed in ISO 8178, Parts 1 - 7.“Mini-dilution” tunnels have been the European and Japanese systems of choice for dilute particulate emissions certification for non-U.S. truck diesel engines. However, repeatability, steady-state test correlation vs. full dilution systems, portability, sampling time, size and system cost have precluded universal industry and regulatory acceptance of existing “mini-system” designs. To address corporate particulate measurement needs, Caterpillar Inc. developed a device known internally as a “Micro-Dilution Particulate Measurement System”. Several major design goals have been achieved: 1) correlation with full dilution systems within ISO 8178 equivalency standards, 2) modest cost (<$100K), 3) short sampling time, 4) reduced setup effort, and 5) excellent portability. A patented porous tube dilution tunnel design provides appropriate sample mixing within an extremely short (300mm) dilution section. Verification of the mixing characteristics has been accomplished via tracer gas testing with a cutaway replica. A proprietary flow controller calibration sequence ensures accurate control and measurement of dilution air and total sample flow. Since the system is a true fractional sampler, it is insensitive to engine size, requiring only a simple stack probe change to provide accurate, representative diesel stack sampling on any size diesel engine.