Non-Road Emissions Standards
Legislation limiting on-road vehicle emissions has become widespread since 1990, with the permissible emissions levels steadily decreasing with successive legislation.
Testing of road-going vehicles is against standardized cycles depending on vehicle type- examples include the NEDC and FTP72/75 for passenger cars, or FTP Transient Cycle for Heavy Duty Diesel in the USA.
Non-road equipment spans the range from small hand held gasoline power tools (often referred to as Small Off-Road Engines, SORE) to large construction machinery. European and US legislation share a common drive-cycle for regulating emissions from Diesel powered non-road machinery. The Non-Road Transient Cycle (NRTC) is designed to take account of a wide range of engine outputs, and the legislation limits emissions of CO, HC, NOX and particulates.
Emissions Development and Compliance
The NRTC is a highly transient cycle, compared with many of the cycles used in on-road testing and certification. This poses engine designers and calibrators with a difficult task. Optimizing an engine for low emissions at steady state involves taking emissions data at a large number of speed/load points, and adjusting parameters such as boost and fuel timing/injection volume to minimize regulated emissions. The requirements to simultaneously reduce CO, HC, NOX and particulates are conflicting, and for this reason the actual process is one of optimization. For example, PM emissions may be reduced by increasing the oxygen available for combustion (further oxidizing the soot particles). Such a move will increase peak combustion temperature and pressure, leading to a sharp increase in NOX. After-treatment solutions, such as Diesel Particulate Filters (DPFs), offer excellent reduction in tailpipe PM, and the opportunity to use high Exhaust Gas Recirculation (EGR) levels to address NOX, but carry a cost penalty, as well as presenting calibration problems of their own.
Conventional Emissions Measurement
The contribution to total cycle emissions from the transient portion of the test is particularly significant on the NRTC, compared with other cycles such as the NEDC. This is due to two reasons- a greater proportion of the NRTC is comprised of transient operation, and these transients are sharper / more aggressive than in the NEDC. No optimization for the NRTC can afford to ignore transient operation.
Conventional analyzers used for gaseous emissions have a response time of around 1 second. This allows accurate resolution of the instantaneous emissions from an engine at steady state, and feedback on the emissions optimization process. During transients, the instantaneous concentrations can change faster than the instrument can respond. Although the correct cycle emissions are measured, these measurements give poor information about the exact engine conditions which correspond to high emissions. They are thus not an effective guide to the engineer or calibration seeking to optimize for a transient cycle
Particulate emissions are legislated on a gravimetric basis- measurements of filter paper mass before and after depositing a proportion of the exhaust flow onto the filter. This technique is therefore inherently offline, and offers no information at all regarding which portions of the speed/load map require improvement.
Fast Response Gas Emissions Analyzers
Cambustion have offered fast response gas analyzers since 1987, and our products are in use in engine test cells around the world. Our gas analyzers use standard measurement techniques, but offer measurements of HC, NOX and CO&CO2 with millisecond T10-90% time response.
In fact this is fast enough not only to accurately resolve transient operation, but even to offer information on each firing cycle of the engine. This is particularly useful on multi-cylinder engines, where significant differences may exist between cylinders (such as EGR mal-distribution) which are difficult to detect in any other way.
Fast Response Real-time Particulate Analyzers
Cambustion's particulate analyzers have been adopted globally since their launch in 2002, offering real-time particle mass and particle size spectra at up to 10Hz, with a T10-90% response time as low as 200ms. Their fast time response makes them particularly suited to developing engines for more transient cycles such as NRTC, as the following example shows.
DPF Testing System
Cambustion's DPF Testing System uses controlled combustion of Diesel fuel to produce soot, and loads this onto a Diesel Particulate Filter. The system can also regenerate the filter, which may be heavily instrumented. The DPG offers a significant reduction in cost and improvement in repeatability over engine based techniques, which it can replace for much of the development process.