Dilution is an additional possible solution to the viscosity problem of vegetable oils as discussed above. Results with this technology have been mixed and engine problems similar to those found with neat vegetable oils as fuels were observed here also. A model on vegetable oil atomization showed that blends of DF2 with vegetable oil should

contain from 0 to 34% vegetable oil if proper atomization was to be achieved (69).

A 75:25(vol-%) petrodiesel / sunflower oil blend had a viscosity of 4.88 mm2/s at 40°С, exceeding the ASTM maximum value of 4.0. The blend was not recommended for long-term use in the DI diesel engine (64). A 75:25 (vol-%) petrodiesel / high-oleic safflower oil blend with a viscosity of 4.92 mm2/s passed the 200 hr EMA (Engine Manufacturers Association) test. The different results were attributed to the degree of unsaturation of the respective vegetable oil (32). The more unsaturated oil (sunflower) that accumulates in the crankcase and hot engine parts tends to oxidize and polymerize due to its reactivity. Accumulation of such products in the lube oil could lead to lubricant thickening. A lube oil change is called for by the EMA test after 100 hr and at that time the viscosity of the lube oils had not varied greatly in either test.

Other reports include successfully using a 70:30 winter rapeseed oil / DF1 mixture (47) or blends of £ 15% rapeseed oil with DF2 (77), and an 80:20 DF2 / safflower oil blend with reduced CO and hydrocarbon emissions (72). A 75:25 DF / crude sunflower oil blend produced greatest solids contamination in the lubricating oil (49) similar to the results mentioned above, while another report mentions satisfactory performance of a 75:25 DF / sunflower oil blend (67). In early studies on sunflower oil, 80:20 DF / sunflower oil blends (31) were run for prolonged periods of time before exhaust smoke increased due to carbon build-up or power loss ensued. Another engine, due to inadequate atomization, showed more of the engine problems associated with neat vegetable oils.

The CP of a 50:50 DF2/ high-oleic safflower oil was -13 °С and the PP was -15 °С, and similar blends with high-linoleic safflower oil had CP -13 °С and PP -15 °С or winter rapeseed oil had CP -11 °С and PP -18°C (55).

A 50:50 blend of Stoddard solvent (a dry-cleaning fluid, viscosity 0.95 mm2/s, estimated CN 50, heat of combustion 46,800 kJ/kg, CP < -16°C, PP < -35 °С, flash point 42.2°C) with soybean oil gave low CP (-18.9°C) and PP (-31.7°C) but performed less well in a diesel engine than DF2 (73).