A direct injection (DI) diesel engine is tested in this work with biodiesel-diesel and biodiesel-diesel cold flow additive blends for emissions at idling conditions. Biodiesel is produced from pure canola oil by transesterification process and the effect of a cold flow additive, Wintron Synergy in different proportions is examined for cold flow property (cloud point) and engine emissions. Systematic tests are undertaken over different engine speeds (800, 1000 and 1200 rpm), with 0, 20, 50 and 100 vol% of biodiesel in biodiesel-diesel and 0.25, 0.5, 1 and 2 vol% of Wintron Synergy in biodiesel-diesel-additive blends. The emission of carbon monoxide (CO), nitric oxide (NO), nitrogen dioxide (NO2), nitrogen oxides (NOx), hydrocarbon (HC), acetaldehyde and formaldehyde from different blends are measured and compared to neat diesel emissions. Test results show that B20S2 has the lowest cloud point of the fuel blends at -34.8 degrees C. Biodiesel and Synergy are found to be effective in reducing both CO and HC emissions. Biodiesel and Synergy content can increase NOx emissions. After warmup, acetaldehyde emissions remain the same for all tests at 5 ppm and formaldehyde emissions increases for all fuel blends and neat diesel. It is also found that Synergy can change the crystal size and structure of biodiesel-diesel blend B20. (C) 2016 Elsevier Ltd. All rights reserved.