In　this　paper,　spray　combustion　of　diesel　(No.　2)　and　diesel-gasoline　blend　(dieseline:　80%　diesel　and　20%　gasoline　by　volume)　were　investigated　in　an　optically　accessible　constant　volume　combustion　chamber.　Effects　of　ambient　conditions　on　flame　emissions　were　studied.　Ambient　oxygen　concentration　was　varied　from　12%　to　21%　and　three　ambient　temperatures　were　selected:　800　K,　1000　K　and　1200　K.　An　intensified　CCD　camera　coupled　with　bandpass　filters　was　employed　to　capture　the　quasi-steady　state　flame　emissions　at　430　nm　and　470　nm　bands.　Under　non-sooting　conditions,　the　narrow-band　flame　emissions　at　430　nm　and　470　nm　can　be　used　as　indicators　of　CH*　(methylidyne)　and　HCHO*　(formaldehyde),　respectively.　The　lift-off　length　was　measured　by　imaging　the　OH*　chemiluminescence　at　310　nm.　Flame　emission　structure　and　intensity　distribution　were　compared　between　dieseline　and　diesel　at　wavelength　bands.　Flame　emission　images　show　that　both　narrow　band　emissions　become　shorter,　thinner　and　stronger　with　higher　oxygen　concentration　and　higher　ambient　temperature　for　both　fuels.　Areas　of　weak　intensity　are　observed　at　the　flame　periphery　and　the　upstream　for　both　fuels　under　all　ambient　conditions.　Average　flame　emission　intensity　and　area　were　calculated　for　430　nm　and　470　nm　narrowband　emissions.　At　a　lower　ambient　temperature　the　average　intensity　increases　with　increasing　ambient　oxygen　concentration.　However,　at　the　1200　K　ambient　temperature　condition,　the　average　intensity　is　not　increasing　monotonically　for　both　fuels.　For　most　of　the　conditions,　diesel　has　a　stronger　average　flame　emission　intensity　than　dieseline　for　the　430　nm　band,　and　similar　phenomena　can　be　observed　for　the　470　nm　band　with　800　K　and　1200　K　ambient　temperatures.　However,　for　the　1000　K　ambient　temperature　cases,　dieseline　has　stronger　average　flame　emission　intensities　than　diesel　for　all　oxygen　concentrations　at　470　nm　band.　Flame　emissions　for　the　two　bands　have　a　smaller　average　emission　area　under　higher　ambient　oxygen　concentration　and　temperature　for　both　fuels,　while　dieseline　has　a　slightly　larger　average　flame　emission　area　than　diesel　for　most　cases.　The　experimental　findings　were　further　analyzed　and　discussed　based　on　an　empirical　model　of　the　distributions　of　air　and　fuel.　Both　experiment　results　and　theoretical　model　show　that　dieseline　has　wider　430　nm　and　470　nm　band　emissions　than　diesel　under　all　conditions.　(C)　2016　Elsevier　Ltd.　All　rights　reserved.