Engine B emissions-control development
An emissions-control system was developed for Engine B operating on LPG using a closed-loop control system and a number of other components (Table 4). To assess the closed-loop operation of the system, SwRI monitored engine air/fuel ratio with a Horiba wide-range sensor, the signal from the control system's EGO sensor, and the duty cycle of the fuel-control valve (FCV). Initial development focused on achieving tight control of air/fuel ratio near stoichiometric conditions. Six calibrations of FCV control parameters were evaluated until the desired air/fuel ratio was achieved.
The upper half of Table 5 shows initial system results, along with open-loop baseline results for comparison. Since the catalyst did not have any run-in time, these data reflect "fresh" catalyst performance. Results indicated that the baseline fuel calibration was on the lean side of stoichiometry, which is standard practice for indoor lift-truck operation. Results also showed that operation in closed-loop control without a catalyst did not significantly reduce emissions with this engine.
Fuel-control calibration was further modified in attempts to achieve lower emissions (lower half of Table 5). Although SwRI researchers were successful with the B-24 calibration in reducing HC emissions, CO and NOx emissions increased. To further reduce emissions, a larger-volume catalytic converter from a Ford Ranger pickup was installed in place of the OEM converter. An emissions test was performed after a 4-h "de-greening" of the catalyst.
Results with the Ranger catalyst with calibration B-6 (Table 5) showed very low emissions rates of 0.13 g HC+NOx/kW•h (0.10 g HC+NOx/hp•h) and 2.82 g CO/kW•h (2.1 g CO/hp•h). However, in subsequent tests it was noted that the B-6 calibration would not consistently control mode 4 to the same air/fuel ratio. The B-24 calibration was re-entered into the engine control module and showed much better repeatability; then another baseline emissions test was performed using the B-24 calibration.
