Emissions of unburned hydrocarbons (UHC) during
starts and stops of gas engine

Jan de Wit og Steen Andersen, June 2004, R0411

English summary (Danish text in the report)

On behalf of the Danish natural gas companies Danish Gas Technology Centre (DGC) has conducted a survey concerning concentrations of un-burned hydrocarbons (UHC) during starts and stops at gas-engine based combined heat and power plants.

Measurements were made at three natural-gas fired gas-engine based co-generation plants. Two of these have pre-chamber gas engines; at the third plant open-chamber gas engines were installed.

Several start and stop sequences were made at each site. At one site also an emergency stop was made.

At a number of plants (pre-chamber gas engines) forced short time ventila-tion of exhaust system has been installed the last years. A significant UHC-concentration reduction due to this was seen from the measurements at one of the two pre-chamber gas-engine CHP plants in this survey. The same significant effect was not seen during measurements at the other site.
The measurements showed peak concentrations close to 35.000 ppm (vol.) for a very short time. This equals some 3% (vol.) unburned gas at the meas-uring point in the exhaust system. The highest concentrations were seen during the stop phase.

The highest concentrations were measured at the open-chamber gas-engine plant. This was a bit surprising due to the fact that this particular engine, when in steady state operation, has low UHC emissions.

Graphs presenting the results concentrations during starts and stops etc. at the different plants can be found in the report enclosures as Figures 1.1, 1.2, 2.1, 2.2, 3.1 and 3.2, the last two mentioned being results for the open-chamber engine.