Which type of powertrain technology is best? A diesel engine or an electric/gasoline hybrid? There really is no simple answer to this question because it depends on what type of vehicle you need (car, truck, SUV), how you use that vehicle (commuting, pleasure, work, towing, etc.), and the relative prices of diesel versus gasoline at the pump.
If you want a truck with lots of towing power, a diesel is the only way to go. If you want a fuel efficient commuter car for urban driving, buy a hybrid car like the Toyota Prius, or buy a turbo diesel-powered car like a VW. If you need a family vehicle but don't want to spend a fortune on fuel, get a hybrid SUV like a Ford Escape.
Unfortunately, your purchase options are limited because hybrid gas/electric powertrains and diesel engines are only available in a limited number of vehicles. More new hybrid models are being introduced every year, so as time goes on you'll have more choices. As for diesels, emissions rules have severely restricted their use to mostly fullsize pickup trucks in the U.S. A few diesel-power cars are currently able to meet the emissions standards, but the cost of doing so is high.
As usual we have the wrong regulations at the wrong time. The EPA decided it would be a good idea to require cars and light trucks with diesel engines to meet the same emission regulations as cars with gasoline engines. The Tier 2 emission regulations, which all cars must comply with start in 2007, require a fleet average of 0.05 grams per mile of oxides of nitrogen, a figure todays diesels cannot meet without low sulfur fuel and electronic direct injection technology. The rules also limit particulate (soot) emissions, which requires diesels to have some type of particulate filter in the exhaust. To make matters worse, California, New York, Massachusetts, Vermont and Maine have all adopted even tougher diesel emission standards than the federal EPA standards.
In Europe, where gasoline costs several times as much as it does here, and where diesel emission regulations are less strict, diesel powered cars account for over HALF the car population. The European limits for oxides of nitrogen are EIGHT times higher than those in the U.S.
In 2006, the only diesel-powered cars available in the U.S. were:
Mercedes E Class E320 CDI
Jeep Liberty CRD
VW Passat TDI
VW Touareg TDI
VW Turbo Diesel Golf TDI
Since then, more diesels options have been added to various makes and models, including Audi A7, A8 and Q5, BMW 328D, Chevrolet Cruze, Jeep Grand Cherokee, and VW Golf.
The main attraction of a diesel engine is that it is more fuel efficient than a gasoline engine: up to 30% better fuel economy as a rule than a comparable gasoline engine of the same displacement. A diesel engine is also much less complicated that a gasoline hybrid, which requires a large heavy battery, electric motor(s), a power inverter to convert the battery's DC (direct current)output to AC (alternating current) for the electric motors, and sophisticated hybrid control system.
A diesel engine uses high compression rather than spark ignition to burn the fuel. This eliminates the need for an ignition system (no spark plugs, coils or ignition module), but it does require a very high pressure fuel injection system, much higher than that on a gasoline engine. Most diesel engines have a glow plug system for cold starting. There is also no throttle on a diesel engine, so it sucks air more efficiently at idle and low rpm (reduced pumping losses). The trade off is that a lack of intake vacuum in the engine requires a separate vacuum pump for any vacuum operated accessories.
On diesel engines, fuel is injected directly into the combustion chamber as the piston approaches top dead center. The timing of the fuel injector is critical for good engine performance. Compression ratios are very high 18:1 or higher, so it takes a LOT of pressure (300 bar to 1800 bar) to inject the fuel into the cylinder or a precombustion chamber in the cylinder head. The heat of compression causes the fuel to ignite spontaneously. That is why no spark plugs are needed.
Mechanically, a diesel engine is essentially the same as a gasoline engine except for the higher compression ratio. Diesels typically have stronger crankshafts, connecting rods and pistons than gasoline engines, and they typically run at lower rpms. Most of these engines are VERY durable and will last well beyond 150,000 miles with proper maintenance. Regular oil changes, however, are essential to maintain a diesel engine because they experience more blowby of combustion byproducts into the crankcase than gasoline engines.
Things that can go wrong with a diesel engine include injection pump problems, fuel injector problems, blown head gaskets, hard starting in cold weather if the glow plug system fails, and fuel waxing. Diesel fuel is actually a very light oil, so if it does not contain the right additives it can gel and plug up the fuel line or filter in cold weather.
Older diesels were also notorious for their idle clatter and black smoky exhaust. Many light truck diesel engines still have those attributes, but most of the direct injection passenger car diesel engines built by Volkswagen are relatively clean and quiet.
Diesels do require a little more maintenance than a gasoline engine, and most owners who want to avoid cold weather starting problems are religious about using fuel additives in cold weather.
Hybrid electric vehicles use a conventional gasoline engine for propulsion, and an electric motor for supplemental power, or to drive the vehicle if it has a full electric mode. The gasoline engine turns an alternator that keeps a large high voltage battery charged. Some hybrids are designed to shut off the gas engine when the vehicle stops moving to conserve fuel. The electric motor is then used to accelerate the vehicle up to a certain speed at which point the gasoline engine restarts and takes over. For maximum acceleration, the electric motor and gas motor may both provide power to the wheels. How the vehicle is programmed to balance gas power and electric power affects overall fuel economy as do driving conditions. That is why a vehicle like the Toyota Prius gets better mileage in stop-and-go city driving than it does on the highway.
On other hybrids, such as the Acura ILX hybrid, Saturn Vue, Honda Insight and Civic Hybrid, the electric motor is used more like a supplemental power source to boost acceleration when extra power is needed. This allows the use of a smaller, more fuel efficient gasoline engine that gets better fuel economy without sacrificing too much performance. The hybrid system on these vehicles is primarily a start/stop system that shuts the engine off to save gas when the vehicle is stopped. There is no full electric drive mode.
Hybrid Vehicles Currently Available in MY2009:
Toyota Camry hybrid
Toyota Highlander hybrid
, Honda Accord hybrid
Honda Civic hybrid
Honda Insight (original model & new model)
Lexus RX400H & GS450H
Ford Escape hybrid
Mercury Mariner hybrid
A vehicle like the Toyota Prius is a technical marvel. But it is also a VERY complex vehicle that is much more complex than any gasoline or diesel-powered vehicle. Consequently, the more complicated the system, the more stuff there is to go wrong.
As long as everything is working fine, a hybrid is a great vehicle to own and drive. But when these vehicles get some miles and age on them, the risk of expensive repairs goes up. Even so, most hybrids come with an extended powertrain warranty (8 years or 100,000 miles in all states except California and several others which require a 15 year or 150,000 mile warranty on the hybrid powertrain components and high voltage battery).
For more information about California's Zero Emission Vehicle and hybrid warranty requirements, Click Here.
Finding a repair shop that is qualified to work on a hybrid vehicle (beyond basic maintenance and repairs) is currently a challenge. In most cases, you have no choice but to take your vehicle back to the new car dealer (which can be expensive) because only the dealer has the training, factory scan tool and parts to diagnose and repair the hybrid components. However, in some areas there are shops who specialize in hybrid vehicle service. Do a local Google search for "hybrid repair" or "hybrid service."
Next-generation hybrids such as the 2011 Chevy Volt took hybrid technology to a new level. The Volt is a "plug-in" extended range electric vehicle. The estimated range in full-electric mode is about 30 to 40 miles. After that, the gasoline engine kicks in, acts as a generator to power the electric drivetrain, and provides a normal driving range of about 350 to 400 miles. You can recharge the battery overnight from an ordinary home 110V electrical outlet. The estimated cost of the electricity for a charge is about $1.50.
The advantage with this approach is that you don't need to run the engine or burn any gasoline at all to charge the battery. Consequently, if you drive the vehicle less than it's maximum range in pure electric mode (less than 40 miles), you burn no gas at all and drive for pennies a day.
Most next generation hybrids such as the Volt and others use smaller, lighter, more power lithium-Ion or Lithium polymer batteries. Lithium Ion batteries are currently used in many laptop computers, digital cameras and cell phones.
Li-ION and lithium polymer batteries provide up to 50% higher energy density than Nickel Metal Hydride (NiMH) batteries, they weigh less, and have a longer service life because Li-ION can withstand over twice as many discharge/charge cycles as NiMH batteries. Li-ION batteries also hold a charge longer without running down if the battery isn't used.
As for diesels competing with hybrids, diesels have their own advantages. The technology has been around a long time, and has more than proven itself in pickup trucks and large trucks. Diesel engines are much better than gasoline engines in thermal efficiency. Their higher compression ratios and ability to run on very lean fuel mixtures allows them to get about 30% better fuel economy than a gasoline engine.
Clean, common rail direct injection technology has eliminated most of the negatives that some people associate with diesels: black, sooty smoke and engine clatter. Common rail direct injection reduces pollution and smoke, and smooths the engine at idle. Direct injection diesel engines run quieter and deliver even better fuel economy than ever before. And with the proper after treatment, they can even meet the EPA's tough new soot and NOx requirements (which require using low sulfur diesel fuel).
Modern common rail diesel engines in European and Japanese passenger cars are as quiet and as peppy as their gasoline counterparts. In fact, most drivers can't tell the difference.
Who says diesels have to be slow? On August 22, 2006, the JCB DIESELMAX set a new land speed record for diesel-powered vehicles with a speed of over 350 mph at the Bonneville Salt Flats, Utah. Powered by two state-of-the-art JCB444-LSR engines developed by Ricardo, the JCB DIESELMAX beat the existing record by almost 100 mph. The race car was powered by two JCB444-LSR engines with two-stage inter-cooled turbo-charging, high pressure fuel injection and a low compression ratio, low temperature combustion system. All of these technologies are being developed by Ricardo for application on the high performance, ultra-low Tier II emissions diesel vehicles of the future.
Diesel Dragster Breaks 200 mph!
The Scheid Diesel Silverline diesel dragster made history at the Muncie Dragway, October 18, 2008 in Muncie, Indiana and is now the official DHRA National Record holder for the fastest diesel powered vehicle in the quarter-mile. Driver Bo Layne made the diesel record-breaking quarter-mile run of 6.908 seconds at 203.71 mph. This is the first and currently the only diesel powered vehicle to break the 200mph barrier in the quarter-mile.
Electric Cars are Best
The original General Motors EV1 electric car.
Long term, the best powertrain choice will be pure electric vehicles, or plug-in hybrids with an extended range. Electric vehicles are environmentally clean, quiet and energy efficient. Fuel costs are potentially equivalent to over 100 mpg at current energy prices. If charged by electricity from cheap wind, hydroelectric or nuclear power sources, the economics make even more sense.. . . . .
In 2007, the Chevy Volt concept for a plug-in electric extended range hybrid vehicle was revealed at the Chicago Auto Show. The vehicle is driven by electric motors and used advanced lithium ion batteries. This is a full electric mode hybrid, and uses a small gasoline or ethanol fueled engine for recharging while driving. The Volt is designed for urban commuters who travel less than 40 miles round-trip. When it is not being driven, the batteries can be recharged by plugging the car into a conventional 110-volt AC outlet. The first production Volts went on sale in late 2010 as 2011 models.
Time will tell how the various powertrain alternatives will play out in the years ahead, but most experts agree that diesel and hybrid vehicles will continue to experience a growing market share. The pie chart below was part of a presentation by Bosch on the future growth of Clean Diesel technology. Bosch says that the 2013 model year will be a big one for the introduction of new diesel-powered vehicles in Europe and North America.
According to the latest Polk Research data, clean diesel car registrations increased by 24.3 percent in the U.S. from 2010 through 2012. Diesel car and SUV registrations increased from 640,779 in 2010 to 796,794 at the end of 2012. During this same period, hybrid car and SUV registrations increased from 1,714,966 to 2,290,903 – a 33.58 percent increase.
The Polk data shows that diesels currently account for 6,658,399 vehicles while hybrids account for 2,295,500 vehicles in the U.S. There are currently 27 diesel-powered vehicle models available in the U.S. market compared to 46 hybrids.
The following chart shows where diesel buyers prevail (source: dieselforum.org):
In 2015, VW was caught cheating on emission tests to make their diesel engines seem cleaner then they really were. VW engineers modified the engine control software so that when the vehicle was given an emissions test, the engine would go into a super-clean operating mode that would allow it to easily pass the test. The software would then revert back to a mode that improved fuel economy and performance but also increased emissions up to 40 times the allowable limit.
As a result of the cheating, VW was fined $2.8 billion dollars and spent upwards of $18 billion more to buy back millions of diesel-powered vehicles from their owners.
VW eventually came up with several "fixes" to reduce emissions, including software upgrades and modifications to the exhaust components on certain vehicles. However, the fallout from the cheating scandal tainted the image of diesels as being a clean alternative to gasoline engines.
For more information, read the updates on the article about Clean Diesel Technology.