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More power? Not hardly, unless the Europeans are dropping the output on their gas engines to make their diesels look more competitive.

Diesels just can’t turn the RPMs a gasoline engine can. It boils down to the mass of the rotating assembly. Diesels run higher compression ratios that give them their efficiency boost, but that higher compression ratio results in a higher mass rotating assembly in the engine. This limits high RPM operation. Additionally, the injectors have to handle on the order of a magnitude higher fuel pressure than the very high pressure injectors now being found in gasoline direct injected engines. Another limit on high RPM. In a diesel, to get equivalent hp as a higher revving gas motor, you have to increase boost pressure at lower RPMs. This increases torque, and therefore horsepower, but it also puts much more stress on the rotating assembly, reducing longevity.

Add in the fact that diesels still have a very real soot problem, and you need exhaust after treatment that goes beyond a simple catalytic converter. This system needs it’s own maintenance/top off cycle in addition to the fuel tank and engine oil.

Also, one more diesel negative -— unburned hydrocarbons. Diesels tend to spew pure diesel fuel into exhaust. It’s part of the soot removal system, but it also means you can never really get rid of the diesel smell completely. It also means that the soot system also has to provide a exhaust cleaning cycle where the oil left in the system is calculated by the computer, and when a preset level is met, the computer has to purposefully light the exhaust system on fire to remove the built up fuel oil.

GDI doesn’t require anything more than a typical catalytic converter. Some GDI engines also have lean burn modes that erase the efficiency gap between diesels and gasoline engines. The lean burn mode allows accurate timing of injector events such that a throttle plate is not needed (the main efficiency drop between diesels and gasoline is the throttle plate at partial loads). Instead, the cloud of fuel is injected at a very precise interval (very short) before spark is applied, and the fuel cloud burns at a stoichiometric ratio, even though a volume of air to volume of fuel ratio for the entire cylinder would indicate far too lean a mixture, such as 60 air to 1 fuel.

Many here will argue, but I would say that diesel will not be a viable road fuel here in the states for *anything* in two decades. GDI or port-injected CNG will replace it in the road going semis and heavy trucks. CNG will probably displace most diesel use in railroad fuels as well. This move would allow the petroleum refiners to have basically one product line for most of America’s land-based transportation system. GDI is even killing the need for various octane levels in fuels, since the computer is not constrained from managing the combustion cycle from the valve event that happens so far ahead of the ignition event in normal port injected gasoline engines. Most people don’t know that 87 octane gas has more energy than 93 octane in most formulations, but that a typical port injected motor can’t take advantage of the extra energy due to the fact that 87 octane fuel pre-ignites more readily in port-injected gasoline engines. GDI has no such problem.