Jun 24 2014
There are two primary benefits of fuel efficiency in the automotive world. As alluded in the title, better fuel economy will both minimize the amount of toxic air pollution and maximize money saved on fuel. Which of these green options is most important to you?
The EPA has been making a valiant effort to raise awareness of the need for more Eco-friendly vehicle solutions. Their message has resonated with many people who in turn have contributed to the environment. But let's face it, many of us drivers aren't nearly as environmentally conscious as we should be.
The effect vehicle emissions have on the environment is much harder to grasp than the visual aid of gas disintegrating on our fuel gauges. As the demand for gas continues to rise, so do the prices, making the need for fuel efficient vehicles a very high priority. To those frequently traveling long distances, it may be just as important of a criteria as vehicle safety.
Given the high value of fuel economy, we've decided to discuss the different options available and how they perform over the next few blogs in the series. Before getting into alternative fuel sources, the assortment of hybrids and electrics, or different bodies and frames, we'd like to first touch base on some of the most efficient vehicles fueled by gasoline and diesel.
Since gasoline is notorious for being the least efficient vehicle fueling option, many modifications have been made to correct this issue. Below are two of the main technologies automotive manufacturers have incorporated to increase fuel efficiency.
One of the more basic ways vehicle manufacturers such as Honda, Toyota, and GM have been able to increase fuel economy is by offering some sort of economy mode that can be optionally engaged by the driver. The functionality between different makes is pretty similar.
In a few of the more recent Honda models including the Civic, Accord and CRV, they come standard with an ECON button which primarily reduces the throttle's power and torque in conditions that don't need the extra horse power. The 2014 Toyota Corolla LE Eco also functions this way. GM's Eco Mode - across different makes and models - increases fuel efficiency by up-shifting sooner, downshifting later, and idling at lower speeds.
Another way that fuel economy has increased in gasoline powered vehicles is by changing the means of fuel injection. As of the 2000's, gas direct injection (GDI) - traditionally used for diesel engines - became a popular option for fuel delivery.
With direct injection, gas is injected at a high pressure directly into each cylinder's combustion chamber through a common rail, instead of mixing with air in the cylinder port like indirect injection. GDI allows for more accurately controlled emissions as well as greater fuel efficiency and horsepower.
Direct Injection engines fueled by gas are starting to become more standard in the auto industry. Some of the current options as of 2014 include models from Acura, BMW, Ford, GM, Honda, Hyundai, Mazda, etc.
Mazda's newer SKYACTIV-G engine has increased fuel economy in the Mazda 3 by about 20% and about 40% in the Mazda 6. Not only does the SKYACTIV engine maximize fuel efficiency, but the lighter more aerodynamic body and energy saving brake system are also contributors.
Ford has created a series of Eco boost DI turbo engine versions first introduced in 2009 and now available on most of their models. And to no one's surprise, BMW offers GDI in almost all of their models.
Variable valve timing (VVT), though not a brand new technology, has also helped to increase overall fuel economy. One of the most commonly known VVT systems is the Honda VTEC, short for variable valve timing and lift electronic control. Honda was one of the first to use this technology, however, many other makes use it and they all function relatively similar. Different camshafts are used to activate the engine valves depending on the speed or RPMs. This allows for a smoother idle at lower RPMs, increasing fuel economy as well as low end power and torque. At higher RPMs, the high performance camshaft is switched on by hydraulic pressure, increasing the overall power.
For those that can recall diesel engines from the 1980s, chances are that the only memories you have are of them being loud, smokey and slow - which doesn't seem to make for a great vehicle. However, the fuel efficiency that diesel offers is much greater than gasoline, since it contains more energy. Similar to gas price inflation back then, the prices now continue to inflate on a whole new level, making diesel an attractive alternative.
Current diesel technology persists to trump the fuel efficiency of gasoline and also incorporates much cleaner systems run by ultra low sulphur diesel, reducing emissions significantly and increasing overall fuel economy.
As mentioned above, direct injection (DI) originated in diesel engines. Given it's more efficient use of fuel, DI is pretty standard for most current vehicles - both diesel and gasoline. The modern way that these systems function is primarily by common rail or unit injection.
With common rail injection, fuel is stored at high pressure in an a fuel-line rail which is connected to all the injectors (one for each cylinder). Fuel stored in the common rail is then transferred to the injectors by a hydraulic valve, which sprays the cylinders at the desired pressure. The latest common rail systems incorporate piezoelectric injectors which are more precise, resulting in better fuel economy.
Unit injection on the other hand combines the injector nozzle and pump into the same unit. This eliminates the need of having a rail to produce the pressure, however, accuracy of timing and control over the amount of fuel injected suffers.
Diesel has been known for its high level of emissions. Though the CO2 emissions are lower than gasoline, the NOx emissions are significantly higher and just as hazardous to the environment. In the newer clean diesel technology, many manufacturers have included diesel exhaust fluid called Urea or AdBlue, which is injected into the exhaust pipeline from a separate tank, cutting down on NOx emissions.
Turbochargers, dating all the way back to the early 20th century, are just now catching as a popular option for passenger cars in North America. Since the sulphur levels of diesel fuel in the U.S were significantly higher than that of diesel in Europe, automakers manufactured turbo-diesel vehicles mainly for European market. As mentioned earlier, ultra low sulphur diesel became available in recent years (2006), making turbo-diesel vehicles an option for the U.S. market.
Traditional diesel engines provide more torque than gasoline engines at lower speeds, but lack in power at higher speeds. Turbocharged diesels allow for extra power at all speed ranges without compromising fuel economy. They also reduce noise and vibration, while making for a smoother ride.
Another option, not as popular as turbo-diesel, is supercharged diesels. Both turbochargers and superchargers function in a similar way by producing more air pressure to the cylinders, increasing the amount of fuel to be burnt, thus increasing the power. However, turbochargers are more efficient than superchargers, since they are only engaged when putting the engine under heavy loads and use the exhaust gases to provide the boost. Superchargers are designed to constantly boost pressures using the engine's power, rather than using a boost threshold like turbochargers. Though there's no lag with constant pressure, the fuel economy suffers.
Since diesel has overcome many of their hurdles, such as excess emissions, noise, and lack of speed; turbo-diesel equipped vehicles are growing in the U.S. automotive market. In 2006, when reduced sulphur diesel became available, European makes such as VW, Audi, BMW, and Mercedes made their diesel vehicles available.
As of 2014, GM has released its Chevy Cruz Clean Turbo-Diesel as well as a couple Silverado truck models and Express vans. Other makes including GMC and Ram have also joined the bunch. Mazda plans to release their SKYACTIV-D models for the Mazda 6 and CX5 in the near future providing that they are able to meet the U.S. required emissions levels.
As you can see, diesel is starting to gain popularity again, and is becoming a more available option. We will discuss Bio-Eco diesel in our next article along with some other alternative fuel options, since Bio-Eco diesel is also becoming a popular option.
Since there's so much valuable information about fuel economy increase in recent years, I'd like to pull out some of the key advances for both gasoline and diesel vehicles that have contributed.
Proceed to the next article Top 3 Alternative Fuel Sources on the MarketAutomotive Technology Article Index