During the June 2016 GRPE session, AEGPL raised concerns regarding the back-to-back approach for the simplified test of retrofitted dual-fuel engines because, in some cases, the hydrocarbons (HC) and/or carbon monoxide (CO) emission values of the original diesel engine are far below the emission limit (see GRPE-73 session report, para. 28). AEGPL proposed a solution in document GRPE-73-07. However the Netherlands is concerned that:

1. The emission performance of the selected diesel engine is not known (above or below the emission limit and how far from the limit);
2. Non-methane hydrocarbons (NMHC) emission cannot be disregarded because NMHC is an important air quality regulated pollutant emission; and
3. The diesel emissions of CO and HC could be far below the emission limit and hence a factor of two would not be sufficient while increasing this factor is problematic.

Contracting Parties and stakeholders have discussed a solution, presented in this proposal, to compare measured emissions of a retrofitted dual-fuel engine with the brake specific emission limits using a CO2 specific emissions approach. This proposal would amend the draft regulation pending before WP.29 (document WP.29/2016/110).