Not since the mid-20th century, when a turbine-powered car for the masses briefly appeared viable, have automotive powertrains been so intriguing. "Powertrain" is the blanket term for the propulsion systems that move your car and truck from Point A to Point B. That includes gas engines, diesel engines, electric motors powered by batteries, electric motors powered by hydrogen fuel cells — you name it.

Here's why it's intriguing. You'd have to flip the calendar pages way back to the late 1800s-early 1900s to see as many production electric vehicle (EV) options as we have in 2013, and more are promised in the coming years. The diesel engine continues to gain respect and chip away at the stigma earned in the 1970s-1980s as U.S. consumers warm up to the newest clean offerings. The push to incorporate domestically produced alternative fuels such as biodiesel, ethanol, compressed natural gas (CNG), liquefied natural gas (LNG), and propane (liquefied petroleum gas, or LPG) into the transportation industry means engines aren't confined to just gas or diesel.

In the modern marketplace, the gas engine is the undisputed popularity king. That makes sense: It has been widely used for more than a century; favorable economies of scale are in place; and 99 percent of all automakers devote enormous R&D budgets to gassers in order to keep this well-established technology relevant and viable by further optimizing its efficiency. But like everything in life, it has its pros and cons. Let's look through a couple different powertrains available today.

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Gasoline engines

Click to enlarge picture2013 Ford Fusion (© Ford Motor Company)

2013 Ford Fusion

As the vastly predominant powertrain technology in use worldwide, the tooling, materials, assembly techniques, maintenance, and repair procedures are conventional and widely understood. The four-stroke, piston-driven gas engine is the most basic model used in introductory auto shop and mechanic training classes, the very first threshold that needs to be passed before graduating to other propulsion methods.

Engines are packed with complex moving parts, but certain modifiable design facets give builders a large degree of optimization freedom. Gas engine performance may be skewed for horsepower or torque, more fuel economy, more performance in the low end of the engine's working range, more performance in the middle of the range, and more performance in the top of the range. Hence, you can find a gas engine in practically every automotive application: small cars, medium-sized cars, big cars, minivans, crossovers, SUVs, and pickup trucks.

Click to enlarge pictureFueling with E85 ethanol fuel mix (© General Motors)

Attendant fueling with E85

Gasoline is easy to find, access, and dispense, with no unusual handling protocols. A single gallon of gasoline contains 33.7 kW-hr of chemical energy. A Ford Expedition with a full 28-gallon fuel tank contains roughly the equivalent energy of an American home's monthly electricity consumption (943.6 kW-hr in the tank compared to 940 kW-hr per home, according to the U.S. Energy Information Administration). It's an energy-dense fuel.

While containing less energy per gallon than gasoline, ethanol fuels are substitutable. The most prominent is E85, which stands for 85 percent ethanol and 15 percent gasoline. It's much easier to find in the Midwest, due to the regional proximity to ethanol's fuel source — corn and assorted grains are the big ones, but farm waste may also be used. Ethanol is more common than you think, and the federal Renewable Fuel Standard program basically guarantees it must be blended into normal gas. Other blends in place include E5 (5 percent ethanol against 95 percent gas), E10 (10 percent ethanol against 90 percent gas), and E15 (15 percent ethanol, 85 percent gas). It's a fringe product now, but you may still be able to find E0 (100 percent gas), depending on your location. Ethanol might help cut down on foreign oil dependency.

Click to enlarge picture2013 Ford Expedition (© Ford Motor Company)

2013 Ford Expedition

Intrinsically, the piston-driven gas engine is thermodynamically inefficient. An extremely optimized engine might be able to turn nearly 40 percent of a gallon of gas' energy into useful work (such as an Atkinson-cycle Toyota Prius engine), but for today's gas engines, anything above 30 percent would be considered more than acceptable. The rest of the energy is lost as friction and heat.

Gasoline engines need routine maintenance. Lubrication oil needs to be changed, seals need to be minded, filters need to be swapped or cleaned, and engines with rubber timing and ancillary belts need these items replaced.

As it's produced from crude oil, gasoline is a volatile commodity subject to price fluctuations. In 2011, the U.S. imported about 45 percent of its petroleum. (Canada and Saudi Arabia are the biggest suppliers.) In the interest of energy independence and security, the U.S. EIA says our dependency on imports has been falling since 2005.

A unit of ethanol contains less specific energy than a unit of gasoline, and the alcohol in ethanol can damage older vehicles' engines and fuel systems if the ethanol mix is high enough. Modern vehicles are designed to tolerate at least up to E10 blends without trouble. Vehicles accepting E85 are normally designated as "flex fuel" ready. As there's less energy per gallon, an engine will typically be downrated in its EPA fuel economy ratings when running on E85 ethanol.

Read: 4-cylinders dominate Ward's 10 Best Engines