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The evolution and explanation of an approach to achieving a stated set of very low emissions limits was described in a previous paper (1)*. The method outlined was to use stoichiometric mixture preparation with EGR dilution in order to employ a 3-way catalyst for low emissions, whilst giving an engine power output competitive with a turbocharged diesel engine. This approach has been followed in an engine development programme, which has resulted in a responsive and driveable engine being produced. The engine has demonstrated the achievability of very low emissions over the US heavy duty diesel transient test (FTP) cycle as follows: The lean-burn approach to low emission heavy duty operation has also been considered, using steady-state engine test results. The NOx-HC trade-off has been identified as a key indicator of engines' potential, and is also considered to give an indication of the accuracy of air-fuel ratio control required to achieve proposed emissions standards.

The development of technology suitable for meeting the CARB Ultra-low- emission-vehicle (ULEV) legislation has now become a main focus for vehicle manufacturers worldwide. This proliferation of interest is mainly a result of the increasing number of eastern US-states currently considering the adoption of CARB legislation and the indication that emission legislation in Europe and Japan for the turn of the century is likely to be of the same severity as CARB ULEV legislation. Current three way catalyst (TWC) emissions control technology suffers from low catalytic conversion efficiency of HC, CO and NOx pollutants during cold operation i.e. before catalyst light off. Cold start emissions generally contribute up to 70% of HC and CO tailpipe emissions during an FTP test. However, in some cases even early light-off of the catalyst, similar to hot operation is not sufficient to achieve catalytic conversion over a test cycle to reach ULEV emissions levels.

A project has been carried out to develop a practical G-DI vehicle with very low emissions; primarily assessed over the European EUDC cycle, but with emissions consistent with ULEV, Euro Stage IV and Japan 2000 legislation whilst maintaining acceptable driveability. A combined test bed and vehicle programme was conducted. Vehicle benchmarking established target emissions reduction areas and testbed work characterised the combustion system. The programme was based on a Mitsubishi Carisma GDI™ vehicle. The vehicle used a prototype Lean NOx Trap (LNT) based aftertreatment system. The Ricardo Vehicle Engine Management Prototyping System (VEMPS) Control System replaced the OEM ECU giving control of drive components and strategies to regenerate LNT of stored NOx were developed. Constant torque during regeneration spikes was achieved. The fuel economy penalty of different regeneration strategies was investigated.