Engine B emissions-control durability
Engine B was installed in an SwRI forklift, with the catalytic converter placed in the exhaust system in the space inside the counterweight. The forklift was used daily for moving fuel drums and other materials. Its operator reported no problems with the modified forklift, and was satisfied with the engine's performance. To accelerate service accumulation, the forklift was placed in service at a local grocery chain's main warehouse, which operates its equipment around the clock, seven days per week. A total of 250 h was accumulated. No operational problems were reported at either location.
The engine was then removed from the forklift and reinstalled in an emissions test cell. The engine was found to be operating lean of stoichiometry in the under 50% load modes. Since the engine was operating acceptably, researchers decided to perform an "as is" emissions test before beginning to troubleshoot the problem. Results are presented in Table 6. Lean engine operation in the lower loaded modes resulted in high NOx emissions.
Following this test, the fuel system was carefully examined and two problems were found. The gas pressure regulator had a small fuel leak, which was repaired by rebuilding it. This had no effect on engine operation. The second problem was a yellowish, viscous liquid coating the inside of the fuel valve. This was the cause of the control problem, and after the valve was cleaned, the system returned to normal stoichiometric control. The control system manufacturer indicated that the problem was likely caused by an additive sometimes added to commercial LPG. Two emission tests were run following the cleaning (these results are also presented in Table 6).
Results showed that low emissions results—meeting ARB's LSI standards—could be obtained on Engine B with a properly operating control system. Results are not equivalent to the 0-h result, but this likely is more due to drift of the hardware and its calibration than to catalyst deactivation. This is reflected by the variation observed between the two stoichiometric 250-h tests.
