Example
An engine using methane-containing fuel may emit some unburned gas.
The catch
Assuming perfect destruction can overstate a project's climate benefit.
Related terms
Methane, Anthropogenic methane, Biogenic methane, Flaring, Fossil methane, Fugitive emissions
In more depth
Methane slip, explained.
Methane slip is the gap between what a combustion device is assumed to destroy and what it does destroy. In gas engines it rises at low loads and during starts and stops, and some engine designs slip more than others. Open flares lose more gas in strong wind. Plants that upgrade biogas to pipeline quality can also release methane in their off-gas.
Shipping shows the stakes. Engines burning liquefied natural gas can emit enough unburned methane to erase a large part of the fuel's expected climate benefit, depending on engine type. A project that assumes complete combustion in its methane-to-energy engines will overstate its results. Ask for slip measured at realistic loads, or a conservative default from an established method.