Many reports on characterization of unregulated exhaust emissions from diesel engines and its measurement methods have been presented, but the number of objective chemical compositions used in those experiments are limited. Those reports have referred to use of a large and expensive full-flow dilution tunnel specified by US EPA, and also to the fact that, in case of a partial-flow dilution tunnel which is called “mini-tunnel”, the use should be limited only to steady state engine operations.
The authors reported in SAE Paper
890181 that a multi-tube type mini-dilution tunnel, which was compact and less expensive, had good agreement with the full-flow dilution tunnel required by US FTP for heavy-duty diesel engines, when the regulated exhaust emissions were measured on a heavy-duty diesel engine under steady state and transient operaton conditions.
In the experiments mentioned in this paper, the authors expanded the range of measured chemical objects up to about 30 components, and found that the results regarding unregulated exhaust emissions from heavy-duty diesel engines agreed well between the mini-and the full-flow dilution tunnels.
This is why the multi-tube type mini-dilution tunnels have been used widely and effectively not only in exhaust emissions tests according to the US FTP but also in unregulated exhaust emissions measurements.
Based on those facts, further exhaust emissions measurements were done, applying the mini-tunnel in combination with some modifications to the analytical method proposed by US EPA, in order to compare unregulated exhaust emissions between a normal diesel fuel and a neat methanol fuel.
While a methanol-fueled direct injection diesel engine with a catalyzer could be identified as a lower emission engine regarding the regulated emission components than a diesel fuel burning engine, it was not clear if it was also true with respect to unregulated emissions because such a small amount of particulate matter emitted from the methanol-fueled engine did not allow accurate analysis of the chemical components. More sophisticated analysis method needs to be developed.