Diesel exhaust fluid with additive

A system for reducing nitrogen oxides in diesel exhaust streams while also reducing the deposition of urea and/or urea decomposition compounds in diesel exhaust systems of engines that use diesel exhaust fluid (DEF) and require selective catalytic reduction (SCR), the system comprising:

• a DEF having (a) about 15 wt. % to about 40 wt % urea, (b) substantially purified water, and (c) a compound additive that generates water in the diesel exhaust streams at temperatures greater than 100° C., interferes with competing reactions that would otherwise prevent decomposition of urea or produce undesired decomposition deposit compounds including biuret, cyanuric acid, ammelide, ammeline, and melamine, or both generates water and interferes with the competing reactions, wherein the compound additive is a sugar;
• a storage vessel containing the DEF;
• a SCR catalyst positioned within the diesel exhaust unit and having a surface;
• and
• a delivery tube connecting the storage vessel to the diesel exhaust unit and delivering the DEF from the storage vessel to the diesel exhaust unit onto or near the surface of the SCR catalyst.