The aim of this study was to establish a fully capable diesel exhaust treatment system (4-way catalyst system) based on a catalyzed diesel particulate filter (cDPF) and a Lean NOx trap (LNT) for meeting US Tier 2 emissions.
In this study, two modified combustion technologies, LTC (Low Temperature Combustion) and PCCI (Premixed Controlled Compression Ignition), were used and improved to achieve high catalyst bed temperatures and to provide rich exhaust gas with low smoke to utilize a 4-way catalyst system. The LTC operation area was expanded to both lower and higher loads using a dual loop EGR system (high-and low-pressure-loop EGR). The effect of air-fuel ratio, injection timing, and intake manifold temperature on combustion stability and soot emissions of LTC were investigated. PCCI, characterized by increased and advanced pilot injection, combined with retarded main injection timings and without EGR was used to achieve low-smoke, rich combustion at medium loads. The effect of pilot and main injection timing, quantity, injection pressure, and EGR rate were investigated to reduce smoke.
For the evaluation, a PSA DW10 diesel (4-cylinder, 2000cc) was used and NOx and CO2 emissions were examined at five points representative of the FTP 75 test cycle.
This study confirmed that LTC and PCCI can facilitate high NOx conversion efficiency with low engine-out smoke, sufficient combustion stability and minor fuel penalty at five FTP 75 representative points (BMEP: 0 to 8.2 bar). Estimated FTP 75 NOx emissions were 0.012 g/mile (fresh catalyst), and estimated CO2 emissions were 1.7% above the baseline. The method to maintain very high catalyst temperatures and provide slightly rich gases was also examined for simultaneous DPF regeneration and LNT desulfation.