This 18% 'less' MPG reflects the difference in the energy density of diesel vs gas.
The two engines are roughly equivalent in converting carbon bonds to usable energy.
That doesn't make gasoline engines less efficient, rather it illustrates how efficient
they have now become. Coupled with the realistic pricing of the two fuels, gasoline
can now compete on an equal footing with diesel at least in lightweight passenger cars.
Now if the car companies could just make the fuel tanks a bit bigger...
Thanks for your input flee. The following comes to mind:
1) See post # 72 regarding the differences in emission equipment required by United States Government law for gasoline passenger vehicles vs. light duty diesel passenger vehicles. Consequently it is not a fair comparison at the moment from this perspective.
2) The efficiency gap between gasoline and diesel passenger vehicles might be narrowing for smaller sedan vehicles that Americans have been abandoning since the 1990s (or even before) in exchange for larger, heavier, less aerodynamic gasoline powered SUVs and trucks with AWD (or similar) as daily drivers. I would not be surprised to see these modern gasoline SUVs/trucks struggling to close the efficiency gap in a noticeable way with respect to their light duty diesel counterparts (I understand not all the models are available in diesel worldwide). And this is without a gas particle filter (GPF) and other emission equipment comparable to the ones in a modern light duty diesel.
3) For those concerned with local air quality please take a look at Argonne National Labs GREET model (https://greet.es.anl.gov/
) which stands for The Greenhouse gases, Regulated Emissions, and Energy use in Transportation Mode. As previous graphs posted in TDIClub forums, the GREET model shows that only electrical passenger vehicles getting their electricity from renewable sources and natural gas have a smaller environmental/health costs than modern diesel passenger vehicles (normalized per mile driven).
There might be other factors to consider such flammable (gasoline) vs combustible (diesel) safety differences in the scenario of a collision, etc.
* Gasoline vs Diesel: do your own independent investigation, the GREET model is becoming more user friendly too
* Electrical vehicles (EVs) in the next ten (10 years) and beyond in the United States will gather substantial rapid momentum:
1) If the cost of fossil fuels at the pump goes considerable higher (for whatever reason(s))
2) The Corporate Average Fuel Economy (CAFE) standards (or similar) stay in place or get tighten further
3) The cost of an average EV with ~ 300 mile range (averaged during the ownership of the vehicle) gets closer to a deal-braker for the average American consumer to buy it
4) The charging infrastructure to support EVs expands considerably outside large metropolitan areas
5) Perhaps other factors?