The best replacement for urea is uric acid.

The best alternatives to urea are rated as following:
★★★★★  uric acid
★★★★  ammonium nitrate
★★★★  ammonia
★★  urine
★  bun
★  creatinine
★  ammonium sulfate
★  uan
★  guanidine
★  urea nitrogen
★  anhydrous ammonia
  nitrate
  thiourea
  anhydrous
  guanidine hcl
  calcium nitrate
  ammonia nitrate
  guanidine hydrochloride
  blood urea nitrogen
  lactic acid
  ammonium cyanate
  fertilizer urea
  ammonium
  dpf
  ammonium sulphate
  def
  phenol formaldehyde

Your alternative for urea is not listed? Suggest!
Speaking about urea, one probably shouldn't forget about diesel engines.

Other search terms related to urea and their ratings are:
★★★★★ diesel engines
★★★ nitrous acid
★★★ diesel
★★★ urease
★★★ sodium hypobromite
★★ lactate
★ humic acid
★ phosphoric acid
★ formaldehyde
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You have in mind a companion for urea and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of urea in all years. Click on graph for more.
urea
uric acid
ammonium nitrate