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Diesel Engines – How Much More Efficient than Gas Engines?

Are Diesel Engines More Efficient Than Gasoline Engines?

Updated October 15, 2018

How much more efficient are diesel engines than gas powered engines? It’s widely been acknowledged that diesel engines get better fuel mileage than gas engines because they are fundamentally more efficient.  Plus, the fact that diesel fuel per unit contains more energy than gasoline doesn’t hurt.  Yes, the diesel engine has some undeniable advantages over gas but the good old gas engine is catching up.

Is Diesel More Efficient?

First, let’s look at efficiency argument. A diesel engine’s higher compression ratio and lean-burn combustion cycle provide an efficiency that no gas engine can currently match. Over the diesel’s operating range, the average “thermodynamic efficiency”—how much actual energy an engine gets from from the fuel—is in the mid 30 percent range, at least 15 percent better than a gas engine.  Big advantage diesel, right? How do you catch that?

The reality is that this lead is shrinking fast. As emissions regulations become stronger and stronger, diesels are slowly losing their edge in the efficiency race.  A big issue is that most of today’s diesel engines need scrubbers that clean up the dirty diesel exhaust. And these systems happen to crimp the overall efficiency of the system due to their design.  They soak up some of the energy that the diesel fuel provides.

And, the gap is shrinking because gas engines continue to improve. Over the past decade, once-exotic efficiency-enhancing hardware such as variable camshaft timing, direct fuel injection and turbochargers have become commonplace on gasoline engines.  And there’s more on the way, like lean-burn combustion and homogeneous charge compression ignition (HCCI, a gas-combustion technology that blurs the line between gas and diesel engine cycles).  There’s little slowing down to search for efficiency in gasoline engines.

Is Diesel More Efficient?

But while their gasoline powered brethren continue to improve, don’t expect the diesel engine to lie down and stay static.  Engineers are working hard to improve the efficiency of diesel engines even more too. The gains will come from hardware such as variable valve timing and independent cylinder combustion control, as well as improved after-treatment systems.

As you can see, the race is far from over.  What is interesting is that while Diesel engines are becoming better accepted over here in the US, they make up over 50% of vehicle sales in Europe.  The reason for this is probably more due to an open mind about diesel engines than pure economics, though.  American manufacturers have made some very poor diesel engines in the past and this has slowed American acceptance.

Source: Lynch Chevrolet

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Calvin Escobar
About Calvin Escobar

The Car scene is so diverse Where I come from, most enthusiasts recognize the amazing engineering (particularly the engines). The bulk of the ridicule originates from the manner in which many of the vehicles are modded/maintained. Thus, the jokes and or hate tends to be aimed more at the owner rather than the machine. All of which makes seeing properly sorted old Toyota's and Hondas at car meets, auto shows, and track days all the more refreshing.

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