Experimental and modelling study of reverse flow catalytic converters for natural gas/diesel dual fuel engine pollution control.

摘要

The desire to reduce urban air pollution and petroleum consumption has renewed interest in the development of natural gas vehicles. The natural gas/diesel dual fuel engine is one of the practical ways to apply natural gas to the conventional diesel engines. Compared to the conventional diesel engines, natural gas/diesel dual fuel engines emit very low NOx and carbon soot to the air. However, poor fuel utilization efficiencies and higher emissions of HC and CO may be encountered at light loads. This study focuses on HC and CO control for the natural gas/diesel dual fuel engines at light loads.; A reverse flow catalytic converter has been developed to complement dual fuel engine exhaust characteristics. This study consists of experimental measurement and numerical simulation of reverse flow catalytic converters. It shows that reverse flow can establish a high reactor temperature even when the engine is run with low exhaust temperature level at light loads. The reactor temperature rise from reverse flow could be two or three times higher than the adiabatic temperature rise, which is based on the reactor inlet temperature and concentration. This temperature allows more than 90% of the HC and CO to be converted with a palladium based catalyst. It proved that the reverse flow is an approach superior to the conventional unidirectional flow to deal with natural gas/diesel dual fuel engine pollution at light loads.; During the engine mode transition, reverse flow could have a special “heat trap” effect. Depending on the HC and CO concentration, it can develop reactor temperature, maintain reactor temperature, or slow down reactor temperature drop. Reverse flow could maintain reactor temperature over 800 K and HC conversion about 80% during 6-Mode test. The reverse flow switch time is evaluated from 5 to 240 second, it shows that the short switch time from 15 to 30 second is good for the engine tested.; A one dimensional single channel model is established to simulate both unidirectional flow and reverse flow reactor performance. The model can simulate the reactor performance with reasonable accuracy. Both CO and methane oxidation over palladium catalyst in an excess oxygen and water are described using apparent first order kinetics. The modified Voltz kinetics is in fact equivalent to first order rate expressions under conditions used in the reactor. The catalyst undergoes an apparent transition at a temperature in the region of 874 K, at which point the apparent activation energy decreased dramatically.