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This paper charts the development of three three-way catalyst (TWC) and four lean-NOx trap (LNT) formulations in four vehicle systems over a four-year period. All LNTs were installed in an underbody location behind a close-coupled TWC on vehicles equipped with either port fuel injection (PFI) or direct injection spark ignition (DISI) engines. In addition to the standard regulatory European drive cycles, a series of steady-state tests were conducted to determine changes in LNT NOx efficiency with increasing NOx storage, and changes in the levels of individual nitrogen-containing exhaust components. Each vehicle system was subjected to a durability cycle up to an equivalent of 80,000 km. The early LNT formulations on systems ‘1’ and ‘2’ suffered from inadequate thermal durability with system efficiencies for NOx deteriorating to ≤ 55% after vehicle aging under lean operating drive cycle conditions (from ≥ 80% when fresh).

This paper describes a series of vehicle emission tests on a port-fuel injected lean-burn engine, to determine the preferred aftertreatment configuration yielding the most efficient regeneration of a lean-NOx trap (LNT). Three configurations were tested: (A) single starter three-way catalyst (TWC) upstream of an underfloor LNT; (B) bifurcated system with short downpipes comprising parallel TWCs upstream of a single underfloor LNT (Y-pipe configuration); and (C) bifurcated system with extended downpipes. System ‘A’ exhibits satisfactory LNT regeneration behaviour, and is within the European Stage III limits after accelerated aging. Results for system ‘B’, with identical TWC and LNT formulations as the single system, show that this LNT cannot be adequately regenerated under standard purge conditions; even with a fresh trap. In this non-optimized bifurcated system, the AFR profile entering the LNT during the rich purge deviates markedly from that requested by the calibration.

A correlation between engine dynamometer- and vehicle-aged catalysts has been established for novel lean-burn applications. A lean-burn, 1.8-L Ford Mondeo with a close-coupled three-way catalyst and an underfloor lean-NOx trap was used for this study. Vehicle aging of the emissions control system was done using a prescribed driving schedule. Engine dynamometer aging was done using a four-event aging cycle modified for lean-burn applications. The two aging methods were compared using maximum NOx conversion efficiencies measured during a two-mode dynamometer evaluation cycle. It was found that 75 h of four-event dynamometer aging is equivalent to 80,500 km of prescribed vehicle driving.

Measurements are reported of heat transfer to a number of non-aqueous liquids that may be used as high temperature engine coolants. Included are engine lubricating oil, propylene glycol and LP 1693. The measurements were made with the coolants flowing at velocities ranging from 0.5-5 m/s in ducts similar in geometry to those employed in cylinder-heads and engine blocks. Heat fluxes up to 100 W/cm2 were used. For most tests the pressure drop across the test section was held constant but a number of tests are reported for constant coolant flowrate. The heat-transfer data obtained are shown to be in good agreement with predictions from the Chen correlation for flow-forced, sub-cooled nucleate boiling. This model is used to evaluate the heat-transfer performance of other non-aqueous coolants, namely ‘Thermex’ and ethylene glycol.