Daniel W. Stewart

New diesel emission control strategy to meet US tier 2 emissions regulations

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 CO 2 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 CO 2 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.

Cycle-Controlled Water Injection for Steady-State and Transient Emissions Reduction From a Heavy-Duty Diesel Engine

A system for co-injecting mixtures of diesel fuel and water into a heavy-duty diesel engine has been developed and evaluated at the Southwest Research Institute. This system features prototype Lucas EUI injectors, full electronic control, and can vary the percentage of water in the mixture on a cycle-resolved basis. Tests of this system were conducted on a production Volvo D-12 engine, and have produced very encouraging results. Water-diesel co-injection yielded a considerable improvement in NOx-smoke and NOx-BSFC trade-offs under steady-state engine operation. In addition, control of the water percentage on a cycle-resolved basis was shown to be an effective method for mitigating NOx and smoke emissions over step-load transients. Results from this work show that a combination of aggressive EGR and diesel+water co-injection is very promising for producing very low levels of engine-out exhaust emissions, reducing the water storage requirements, and improving fuel efficiency. Further refinement of this injection technology is in progress.Copyright