Just why does a Diesel engine get better fuel economy than a gas engine? Well, they work differently and burn different fuel, for starters. A gasoline engine uses a spark ignition system and a Diesel engine uses the heat created by a very high compression ratio to ignite the fuel. There is actually work underway, by Mercedes Benz and others, to operate a gas engine using diesel-like compression ignition, for at least a portion of the time.

There are a few reasons for the increased of most diesel engines when compared to gas engines. One reason for the lower fuel consumption is that diesel fuel has a higher energy density than does gasoline. For example, standard diesel fuel has an energy density of approximately 139K BTU per gallon. On the other hand, gasoline has fractionally less energy, about 125,000 BTU per gallon. As a way of comparison, much touted ethanol is far below either of these two, at about 85K BTU / gallon. That means that a gallon of diesel there has a greater ability to provide propulsive energy, if the efficiency of combustion is equal.

There is another primary reason that diesel engines tend to get better fuel economy than a gasoline power plant. This reason is due to the fuel delivery system of diesel engines; direct injection. Direct injection is more conducive to ensuring all the fuel atomized and is burned. Obviously more complete combustion leads to greater efficiency and lower fuel consumption. The same reasons have led to direct fuel injection systems being adopted for gasoline engines from various auto makers, including Cadillac, Saturn, Audi, and Pontiac. Expect to see wider adoption of this technology on gasoline engines in the near future as a way to decrease emissions and save fuel.

Differences in Power Delivery Between Gasoline and Diesel Engines

A diesel engine tends to develop power lower in the RPM range than an a comparable gas engine. In addition, the diesel will usually develop more maximum torque but less horsepower than a gasoline engine. This means that depending upon the use, the actual fuel economy figures from both gas and diesel engines can be very different indeed. Diesels are typically excel at lower, more constant speed operation while pulling heaver vehicles, while gasoline engines are better suited to lighter vehicles, variable speeds and rapid acceleration.

That partially explains the widespread use of diesel power plants in trucks. They will deliver much higher fuel economy than a comparable gasoline engine when towing heavy loads, and more easily climb steep hills when doing so. There are also durability advantages to diesel engines, especially in heavy duty applications. The operational differences between diesel and gas engines also helps explain the really high highway fuel economy figures returned by passenger cars with small, turbo diesel engines, such as the TDI powered VW Jetta (41 EPA Hwy MPG).

That’s why a diesel engine get better fuel economy than a gas engine.

Until next time………

What is a hybrid car? Even with the myriad new coverage and the copious advertising for hybrid vehicles, the fact is that many people are unsure what one really is or how hybrids work. As the name suggests a hybrid car (or any other hybrid vehicle) is one that uses a combination of two power plants to increase fuel economy and reduce emissions.

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In the majority of cases hybrid vehicles use a gasoline engine and one or more electric motors. Some manufacturers are developing hybrids that use a small, high efficiency, turbo diesel engine in lieu of the gas engine. Using a turbo diesel as part of the hybrid power train will have advantages in efficiency, emissions, and the ability to use renewable biofuels. The manufacturers developing diesel / electric hybrids are principally European, which makes sense given the popularity of diesel vehicles in Europe. So far Citroen, VW, Opal, and Peugeot have all showed prototype vehicles that have strong production possibilities.

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The hybrid’s electric motors draw their power from a large battery bank in the vehicle. This is recharged either from a generator connected to the gasoline engine, or by a process known as regenerative braking. The regenerative braking is merely recapturing the energy contained in the vehicle because it is moving. Any object that is moving required energy to get it moving at the speed that it’s traveling and maintain that speed. To slow it down, the energy must be removed.

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With a normal vehicle, friction brakes are used for slowing and stopping. These transform the energy contained in the moving vehicle into heat, which is then dissipated into the air. If that seems like a complete waste, it is. The hybrid’s regenerative braking systems actually recapture that energy and store it in the batteries used to power the electric motors for later use. There are one or more generators that are coupled to the wheels under braking. The drag created by the generators when turning the car’s spinning wheels into electricity provide much of the stopping power. This has two benefits; greatly increased brake life, and capturing energy that would have been wasted as heat (and that you already paid for).

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Because internal combustion engines such as gasoline and diesel engines exhibit increased efficiency during different operating conditions, the vehicle can be operated on the optimum power source for a given load condition. At times such as peak acceleration, both power sources can be used in combination. Electric power is typically used when starting out and at low speeds when electric motors are most efficient. The internal combustion engine takes over at higher speeds or when the batteries are discharged.

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There are different types of hybrids. Pure hybrids can move completely on electric power. This can be kind of weird if you’re not expecting it. The first time I experienced this, a Ford Escape hybrid pulled away from a stop as I was standing next to it. It was eerie as the truck silently glided away from the curb, as if by magic. After it was moving about 10 mph, the gas engine kicked in and it motored (engined??) away.

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The stored energy in the batteries let the hybrid’s engine be completely shut down when stopped. The engine is only restarted after the vehicle’s electronic control unit decides it would be better to let the gas engine handle things. More efficiency is gained by using this method. This is similar to the technique used by your internal combustion powered golf cart, but far more sophisticated.

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In fact, the sophistication of engine and control electronics are one of the reasons that practical hybrid vehicles are on the road today. Juggling the optimum mix of power between the two power systems, and recapturing the heretofore lost energy from the moving vehicle would have been impossible to accomplish affordably and practically a few years ago.

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So, that’s what a hybrid car is and kind of how it works. My favorite is the Honda Civic hybrid, followed by the Chevy Tahoe Hybrid, but I’m waiting for someone to make a really cool sports car hybrid, which reportedly Toyota is doing as a replacement for the dear, departed Supra. Toyota probably has more experience than any other manufacturer with hybrids, so they should be well equipped to handle such a task.

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Not to be outdone, Honda is reportedly releasing their CR-Z in about 2011. The CR-Z is a sports coupe in the same vein as the Honda CR-X of 15 years ago, but with a sexy, modern body, great handling, and the hybrid power train from the new Civic hybrid.

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Until next time……..

As diesel fuel hovers between $4.50 and $4.95 a gallon, knowing how to improve diesel fuel economy is likely right at the top of your list, weather you drive a new Diesel Jetta TDI or a Chevy 2500 with a Duramax. If you are averaging over 40mpg in your new Jetta TDI, you may not have the same yearning for that knowledge as if you just finished pumping about $150 worth of Chevron’s finest into the saddle tanks of your 3/4 ton tow rig, but you get the point nonetheless.

With that in mind, here are some tricks you can use to get better fuel economy out of your diesel, weather you use it for towing, long freeway cruises, or just drive to work everyday like the rest of us poor slobs.

Diesel engines are internal combustion engines like gasoline engines but there are some important differences, the main one being they have no spark ignition system and burn a more oil-like fuel. The lack of an ignition system minimizes maintenance, such as the requirement to change spark plugs, spark plug wires, distributor cap and rotor, because there aren’t any! Most modern cars have eliminated all these parts except for the plugs themselves anyway by going to a coil-on-plug ignition system. If you’ve ever had to replace your coils on one of the new cars, you’ll probably long for the good old days of a traditional distributor that you could pick up at any auto parts store for $20.

Diesel engines use direct fuel injection systems. These inject the fuel directly (Hey, imagine that!) into the combustion chamber where it’s ignited by the heat produced by the diesel engine’s extremely high compression ratio. Some new gasoline engines, such as the new Cadillac 3.6 liter V-6, 2009 Porsche flat 6 engines, and the newer Audi engines are also using the direct fuel injection technique, combined with the gasoline engine’s spark ignition systems, to gain efficiency and maximize fuel economy.

So if you are driving an oil burner, how can you stretch every last mile out of a thankful?

For diesel powered vehicles many of the same fuel saving techniques apply as are used for gas powered vehicles; drive slower, clean out excess weight, don’t have a loaded roof rack if you don’t need to, keeping tires properly inflated, etc. There are some diesel specific fuel economy tricks, however that can be used to really make your gas powered brethren a bit jealous as you bypass the gas station.

How to Maximize Diesel Fuel Economy –

Learning how to correctly drive a diesel engine for the best fuel economy is very important, especially if you’ve spent your life behind the wheel of gas powered vehicles. Diesels just work a bit differently, and have about half the rpm range of a comparably sized gas engine. You’ll usually be turning much lower rpms on the freeway when driving a diesel powered vehicle, and that’s just the way these engines like it.

Use the cruise control –
One of the reasons that diesel engines are often chosen for duty in heavy commercial applications such as generators and pumps is that they like to be operated at a constant speed, and are most efficient when run that way. Remember that in your daily driving. Find the rpm that your engine is the most efficient for a given load and stay there. Use your trip computer to find the best instant mpg speed at the load ranges that you normally use and chart them. When traveling on the freeway set your cruise control for these speeds.

Short shift the engine –
Short shifting is a driving technique for manual transmission vehicles where the engine is shifted into the next gear well before its power peak and red line. For drivers that are accustomed to driving gas powered vehicles this may seem counter intuitive, but diesels typically don’t like to spend their time in the upper reaches of the tachometer. Shift at maximum torque point, which on diesel engines tend to be fairly low in the RPM range.

Choose a lower final drive –
If you’re buying a new pickup or SUV with a diesel engine option, you’ll often have a choice of different rear end (final drive) gear ratios when perusing the option sheet. Unless you’ll be spending most of your time towing very heavy loads (6,000+ lbs.), choose the lowest numerical ratio that’s available. If you’re searching for the best fuel economy, the lower (numerical) gear will really help you get it.

Don’t buy bargain basement diesel fuel –
Diesels are very sensitive to the quality of their fuel. One of the worst things you can do is feed them contaminated fuel, especially if it contains water. Steer clear of the low budget stations. The few cents a gallon you save could come back to bite you.

General Motors actually issued a technical service bulletin (TSB) relating to fuel economy in its diesel powered trucks. This would apply to most other brands of diesel trucks, in addition to SUVs and cars. Here are the factors listed in the GM TSB that can affect diesel powered fuel economy:
• Accessories that increase wind drag. Keep the bike rack, or ski carrier off your rig when you’re not heading out to the mountain. This is especially harmful to the mileage you’ll get in a diesel car with a smaller engine, as it causes it to work much harder than the same wind resistance increase on a big-engined diesel powered rig like a Duramax or Cummins pickup.
• Driving 65mph will lower fuel mileage up to 15% as compared to driving 55. This is especially true when towing a heavy load that has poor aerodynamics and a large frontal area, like your big wakeboarding boat with a tower.
• Frequent stops, changing speeds or otherwise poor driving habits. Diesels love steady state operating conditions and prove it by returning their best fuel economy when operated that way. Find the best fuel economy speed for a given load and just set the cruise control for that speed.
• Transmission problems such as OD automatics not shifting into OD, or the lockup torque convertor not locking up.
• Fuel system problems such as contaminated fuel filters. The fuel filter on a diesel is even more important than on a gasoline engined vehicle. Make sure the water separator is functioning properly.
• Final gear ratio. As noted above, when purchasing a new truck check the option box for the lowest numerical ratio possible unless you’ll be spending a significant portion of your time towing heavy loads, in which case you’ll want to go to a lower (higher numerical) gear ratio in the rear end.
• GVW (Gross Vehicle Weight).
• Wheel alignment and tire pressure – check your alignment and tire pressure. If either of these are out of adjustment or spec, it increases rolling resistance and reduces fuel economy.
• Misadjusted or dragging brakes – the same as above. In addition, make sure you don’t ride the brakes when driving. This behavior is fairly common, as evidenced by the dodos cruising down the freeway with their brake lights on.

Using diesel fuel additives –
Diesel engines burn a very different fuel than gas engines. One of the most important ratings that describes diesel is its’ cetane rating. Cetane is a measurement of its propensity to burn and support combustion; to a point, the higher the better.

Most commercially available diesel fuel runs around a 40 cetane rating. Not bad, except that most diesel engines found in pickups, such as the Duramax, Cummins, or Powerstroke like about 5 – 10 points higher than that. One way to raise the cetane rating of what you put in your tank is through the use of fuel additives. Diesel additives will also increase the lubricity of the fuel to help protect engine components and decrease internal friction. Both of these effects will increase your diesel’s fuel economy.

Take a look at the post I did last on the 3 best car modifications to increase gas mileage. The same 3 mods apply for diesel vehicles, and for many of the same reasons. In fact, one of them, reprogramming your diesel’s ECU, is one of the favored mods to radically increase your diesel’s power and torque too. The sophistication of the new controllers is pretty phenomenal. They can allow you to select different settings depending on your current use. If you’re towing for example, you can just dial up more grunt, but keep more conservative programming for daily driving to save fuel. They can even tell if your transmission is slipping and reduce the fuel to save your tranny.

This is a beginning primer on how to maximize fuel economy for your diesel powered car or truck. Since better fuel economy is one of the main reasons people buy diesel vehicles, there is a bit of gold in here.

Until next time.