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At this point they seem about equal:
As of 2010, the density of petroleum diesel is about 0.832 kg/L (6.943 lb/US gal), about 11.6% more than ethanol-free petrol (gasoline), which has a density of about 0.745 kg/L (6.217 lb/US gal). About 86.1% of the fuel mass is carbon, and when burned, it offers a net heating value of 43.1 MJ/kg as opposed to 43.2 MJ/kg for gasoline. However, due to the higher density, diesel offers a higher volumetric energy density at 35.86 MJ/L (128,700 BTU/US gal) vs. 32.18 MJ/L (115,500 BTU/US gal) for gasoline, some 11% higher, which should be considered when comparing the fuel efficiency by volume. The CO2 emissions from diesel are 73.25 g/MJ, just slightly lower than for gasoline at 73.38 g/MJ.[23] Diesel is generally simpler to refine from petroleum than gasoline, and contains hydrocarbons having a boiling point in the range of 180–360 °C (360–680 °F). The price of diesel traditionally rises during colder months as demand for heating oil rises, which is refined in much the same way. Because of recent changes in fuel quality regulations, additional refining is required to remove sulfur, which contributes to a sometimes higher cost. In many parts of the United States and throughout the United Kingdom and Australia,[24] diesel may be priced higher than petrol.
And:
Diesel engines are lean burn engines,[31] burning the fuel in more air than is needed for the chemical reaction. They thus use less fuel than rich burn spark ignition engines which use a stoichiometric air-fuel ratio (just enough air to react with the fuel). As Professor Harvey of the University of Toronto notes, "due to the absence of throttling [constant amount of air admitted, per unit fuel, with no user-determined variation], and the high compression ratio and lean fuel mixture, diesel engines are substantially more efficient than spark-ignited engines", generally; Harvey cites the side-by-side comparisons of Schipper et al. and the estimates of >20% lower fuel use and (given differences in energy content between fuel types) >15% lower energy use.[32] Gas turbine and some other types of internal combustion engines, and external combustion engine, both can also be designed to take diesel fuel.
and more:
Chemical composition
Diesel does not mix with water.
Petroleum-derived diesel is composed of about 75% saturated hydrocarbons (primarily paraffins including n, iso, and cycloparaffins), and 25% aromatic hydrocarbons (including naphthalenes and alkylbenzenes).[54] The average chemical formula for common diesel fuel is C12H23, ranging approximately from C10H20 to C15H28.[55]
Chemical properties
Further information: Diesel exhaust and Gel point (petroleum)
Most diesel fuels freeze at common winter temperatures, while the temperatures greatly vary.[56] Petrodiesel typically freezes around temperatures of −8.1 °C (17.5 °F), whereas biodiesel freezes between temperatures of 2° to 15 °C (35° to 60 °F).[56] The viscosity of diesel noticeably increases as the temperature decreases, changing it into a gel at temperatures of −19 °C (−2.2 °F) to −15 °C (5 °F), that cannot flow in fuel systems. Conventional diesel fuels vaporise at temperatures between 149 °C and 371 °C.
Conventional diesel flash points vary between 52 and 96 °C, which makes it safer than petrol and unsuitable for spark-ignition engines.[57] Unlike petrol, the flash point of a diesel fuel has no relation to its performance in an engine nor to its auto ignition qualities.
BUT I cannot find the temp needed to convert it to 100% vapor and rater diesel has much less additives.
Rich
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