Exhaust Gas Emissions and Piston Wall Temperature under Transient Operation in a Small Diesel Engine.

Abstract

Diesel combustion and exhaust gas emissions under transient operation (when fuel amounts abruptly increased) were investigated under a wide range of operating conditions by using a newly developed gas sampling system. The relation between gas emissions and piston wall temperatures was also investigated. The results indicated that NOx, THC and smoke showed transient behavior after the start of acceleration before reaching the steady-state condition. Of the three gases, THC was most affected by piston wall temperature ; its concentration decreased as the wall temperature increased. Criteria cycle numbers, at which gas concentration reached a steady-state value after the start of acceleration, were about 1. 2 times the cycle constant (τ*) of the piston wall temperature for THC, and 2. 3 times in the case of smoke. A slight increase in NOx concentrations immediately after the start of acceleration resulted in increased premixed ROHR. This was caused by a temporary increase in ignition lag under increased wall temperatures. © 1995, The Japan Society of Mechanical Engineers. All rights reserved.