Diesel engines are built like the standard gas engine with the exception that its ignition cycle is different. Diesel engines follow a process where it takes air first, then compresses it to a point where its temperature goes up drastically because of the extreme pressure, then it afterwards squirts a small amount of diesel fuel into the chamber which instantly combusts on contact with the heated air.

Gasoline engines on the other hand mix the gasoline and air first, then compress it to a higher temperature together. Once it hits the highest point, a spark plug ignites the mixture, generating energy.

This is the reason why diesel engines are conventionally larger than gasoline engines. They have larger pistons to draw in larger amounts of air. The more air they draw in the more air it can compress, which will generate more heat and burn diesel more efficiently.

Diesel engines used take time to warm up on first startup. This is because it lacks a throttle. Diesel engines regulate combustion by controlling the amount of diesel sprayed into the combustion chamber. Gasoline engines control the amount of air into the engine (throttle). The lack of a throttle allows a larger amount of cold air enter the combustion chamber of a diesel engine. Gasoline engines have the added benefit of using spark plugs to ignite the fuel.

Fortunately, modern diesel address this challenge by using a tandem of glow plug or a heating element that uses the car battery to ignite the fuel and electronic fuel injection (EFI), thus quickly heating the engine.

How Diesel Engines are Fuel Efficient

Advantages:

Diesel Engines can save money alone directly from the price itself. Diesel fuel prices at the pump are usually lower priced than the cost of gasoline. For the US, for light pickups and SUVs that can translate in a saving worth 1500 to 2500 USD every 100,000 miles, depending on load.

Lower fuel consumption. Pound for pound, diesel engines consume less fuel than gasoline engines. It becomes more fuel efficient if it is a turbodiesel.

Fuel efficient even in idle. Diesel engines can be left idle for hours and even days. Its lack of an air throttle attributes to its efficiency compared to idling gasoline engines.

Upgradeable. Diesel engines are mostly overbuilt already and are already designed to withstand higher than usual stresses. It is not unusual to see diesel engines modified with turbochargers or superchargers since they’re designed to suck in more air therefore more power to the engine.

Less carbon monoxide. Compared to gasoline engines, diesels produce less carbon monoxide as diesel engines burn.

Disadvantages:

Heavier and bigger. Diesel engines are bigger than gasoline engines partly because it has to have bigger pistons to suck in air from the outside for a more efficient burn.

Diesel burn. Because diesel is spray the moment air is compressed, not all diesel will be able to strike superheated air molecules, resulting in some unburned diesel depending on its quality. This will result in soot out of the exhaust. However, the engine still performs more efficiently than gasoline engines.

Noise. Diesel engines make more noise than gasoline engines, especially on cold startups.

Alternatives:

Diesel engines can be further made more fuel efficient, powerful, silent and environmentally friendlier with the attachment of a hydrogen generator system or similar device.

People saw that big engines were very inefficient and they started looking for new solutions. The answer to the large gasoline engines were rather small, turbo powered diesel engines.

Until then diesel engines have been used mainly on heavy-duty machinery and large trucks, but scientists began to install them on small cars for their fuel efficiency and cost savings.

Diesels are still considered by some people as noisy, unreliable and expensive to maintain, but things have evolved greatly since the early days of the diesel engine. General Motors was among the first companies to fit diesel engines to cars like Chevrolet Caprice and the Oldsmobile, but these engines were shaky and very unreliable. GM soon admitted they had been doing things wrong and re-fitted those cars with normal gasoline engines. It was a large image hit and that is why consumers are still very reluctant to buying a diesel-powered car today.

Diesel engines also cause a bit more pollutant than comparative gasoline engines and with the taxes on polluting cars growing every year, no body wants to pay more taxes for their car if they can buy a gasoline engine car and pay less from the start.

Car companies also have looked at how they can optimize power output of modern diesels and how these engines can be made greener and they have came out with modern solutions.

European car makers have been putting diesel engines in their cars for many years now and in Europe more then half of the cars sold are diesel powered. Manufacturers like Volkswagen, Mercedes or BMW are selling their large limousines mostly with diesel engines, for their power efficiency and cost savings when it comes to mileage. However, not only large cars have been fitted with diesel engines in Europe, but also sports cars. Audi, for example, is producing a 500-horse power sports car fitted with a V12 diesel engine. In addition, they claim this engine to be more powerful, greener and more efficient than its gasoline counterpart does.

Car manufacturers, especially in Europe and Japan, have been fitting large SUVs and 4×4 with diesel engines mostly for decades now. Fitting a gasoline engine on a large 4×4 would mean that its mileage would be extremely bad and its taxes would overcome its owner.

However, modern diesel engines are very powerful and a lot more reliable than they have been 20 or 30 years ago. Car manufacturers all over the world offer the same warranty for its diesel-powered cars like they do on their gasoline cars and this proves that modern diesel engines have the same reliability as gasoline engines have.

Within diesel engines, air and gas are equally infused into the motor at various stages, as opposed to gasoline where a combination of air and gasoline are presented. The gas is shot into the diesel utilizing an injector where in a gasoline engine, a carburetor was used for this very purpose but now also utilizes an injector.

With gasoline engines, gas and air will be directed into the motor along at the identical time, then compressed. The air and fuel combination will limit fuel compression, and in so doing hence the general efficiency. Diesel engines only compress air, and the ending ratio is usually greater.

Strengths Diesel motors are generally a lot more efficient and preferable when compared with gasoline engines as a result of subsequent factors:

1. Diesel engines have overcome the various disadvantages involving earlier designs that featured greater noise and maintenance costs. Currently, they are quiet and necessitate less regular maintenance when compared with gas motors of a comparable size.
2. Diesel motors are more rugged and dependable.
3. There is no sparking whatsoever when the fuel ignites. The absence of spark plugs and wires also helps to reduced maintenance cost.
4. The fuel cost produced by efficiency is 30 – 50 percent lower than gas engine fuel prices.
5. Gas burns hotter compared to diesel, and consequently they have a smaller expected life when they are compared with diesel engines.

Better Gas Mileage

These days everyone is looking at the price of gasoline so that they will be able to save money. There is a misconception about diesel gasoline because it costs more at the pump that other kinds. While it is a little more expensive, it is important to remember that the engine actually runs more efficiently than other kinds of engines. This is why you will be able to enjoy three times the gas mileage of a normal engine. While you will pay a little bit more at the pump than you will for normal gasoline, you will end up saving money in the long run because you make less trips to the pump.

This kind of gas mileage comes in vary handy when you are going on long trips. This is exactly why the trucking community uses diesel engines almost exclusively. There is another reason why diesel engines are used by the trucking industry. The engines are better suited to producing steam and hydraulics. These are things which are used all the time in the trucks so that they will be able to power the brakes, steering and many other properties of the engine. This is just one of the many reasons why truck engines are diesel engines.

Cleaner Burning

There are a few different reasons why the diesel engines are cleaner burning than the regular engines. The first reason has to do with the type of fuel itself. This is because the gas is burning at a much higher temperature than normal gasoline does. This eliminates many of the pollutants which the gas can release into the air. The result is that you do not see any black smoke coming from the back of diesel cars anymore. This is in part because of better filtration systems in the car for the exhaust. It is also because of more efficient usage of the fuel itself.

Getting Gas

The most difficulty people with diesel engines run into is finding gas stations which sell the diesel fuel. This is because the industry is still trying to get used to the fact that more car manufacturers are using this type of engine than ever before. At best you will be able to find one pump available at most locations which sell the fuel. This is sure to increase in the future as more car makers turn to this kind of engine. This will happen as more people find the benefits of the diesel engine.

Turbocharging is the method with internal combustion engines to use a vehicle’s exhaust gases to cram force-induced compressed air into the engine. This concept follows the idea that a normal internal combustion engine’s ability to use air to power a combustion cycle is limited to the negative pressure its pistons creates to draw air in from the outside unaided.

However, with the turbocharger, more air mass is forced into the engine, thereby making the engine burn much more efficiently, and hence performs much better.

Comparatively, turbochargers are used more often in diesel engines due to the following characteristics:

-Normal diesel engines are designed to be over-built, helping it withstand higher pressures and heat from the start.

-Diesel engine power outputs are less compared to gasoline engines which require less pressure from turbochargers to produce more power.

-Diesel engines are not limited by the octane ratings of gasoline as diesel engine are designed to pump fuel into its combustion chamber only at the moment of ignition.

-Are proven to be fuel-efficient than diesel engines with no turbocharger. In diesel engines, more air compressed into the engine results in greater fuel efficiency.

Practically, there is little downside to owning a turbodiesel vehicle.

Turbocharged gasoline engines, though, may perform better than turbodiesels but require more consideration for balance and maintenance.

On the other hand, installing turbochargers in gasoline engines have the following caveats:

-Gasoline engines are lighter than diesel engines. Forcing air into engines has the added effect of “overclocking” the engine, increasing heat and pressure above normal specifications.

-Adding a turbocharger to a car is more expensive than buying a car with a stock turbocharger as upgrades to other parts of the car are needed to bear the added heat, pressure, torque and power.

-Gas turbochargers have to take into account the octane ratings and autoignition temperatures of its fuels.

-Gasoline engines spray gas and air into the combustion chamber at the same time it is being compressed. The act of compressing the air with already compressed air from the turbocharger may detonate a low octane gas prematurely.

-Maintenance is high, which limits gas turbochargers to high performance vehicles.

So how can I turbocharge my vehicle more fuel efficient without spending so much more?

Buy a turbodiesel. Hands down turbocharged diesels have the advantage by the price of diesel nowadays, the very design of diesel engines, and the way it saves diesel the more air you pump into the engine! Turbodiesel vehicles have a good resale value so don’t expect rock bottom prices, but expect years of good use from even an old turbodiesel. Best value for money!

Buy gasoline vehicles with turbo already installed. Face it. Unless you’re a car enthusiast, installing a turbocharger in a car will cost you too much!

Buy smaller gasoline vehicles with turbo installed. There are smaller vehicles in the market that sell units with turbochargers to maximize the small size of the engine. Look up units in the Volvo and Saab lines.

Consider alternative fuels. You can use alternate fuels such as a hydrogen-on-demand (HOD) system to supplement a smaller turbocharger and engine tandem. This system creates hydrogen (H2) and oxygen (O2) gas on demand from a water medium to mix with the air and fuel in the combustion chamber for even better performance.

What does a HOD system do?

Hydrogen when compressed and introduced to an internal combustion engine:

-Releases more energy than ethanol-based mixes, maintaining the overall power of the car

-Burns the fuel more completely which gives cleaner emissions

-Raises the octane level of the fuel, preventing knocking, making the engine quieter

-Lowers overall engine temperature slightly

-Requires the engine to use less gas per cycle

Is it safe?

HOD systems generate hydrogen only on demand and are therefore safe. When no electricity is routed through the HOD system, no reaction is generated. No hydrogen is in storage in this system but is kept in medium, which is basically water.

Cost?

Parts are sourced from everyday parts found in hardware shops and basic electronics stores. Total cost for a basic unit can range between $70 to over $200 USD.

What’s offered by most HOD enterprises are plans for do-it-yourself systems, with offers to build the system for the consumer if they so wish. This way the customer can opt to build it himself or to buy a unit once the concept is understood after obtaining the plans to prevent fraud.

More Power: A turbodiesel engine can produce much more peak torque than a gasoline engine of equal size, and maintain peak torque over a broader RPM spectrum.This provides for much more power throughout the operating range, less downshifts for improved fuel economy, and increased payload ratings.

Higher Towing Capability: Due to the stout structure and additional torque of a diesel engine, payloads on diesel powered trucks are much higher than those on similarly sized gasoline V8 powered trucks. If you have something large to tow, a diesel will make the task much easier and provide the best fuel economy possible while loaded.

Aftermarket Support: Diesel powered trucks are receiving much more attention from the aftermarket than gasoline powered trucks due partly to the fact that diesel engines are easy to tune for more performance. Where a few simple bolt on parts may increase your gas powered truck’s performance by 50-75 horsepower, the same parts could take your diesel to extreme performance levels. How does an additional 200-350 horsepower sound? (Based on performance testing of a tuner, cold air intake, and exhaust system; the three most common and readily available engine modifications.)

Driving Experience: If your any sort of automotive enthusiast, or just like a truck that can run through the gears fast, diesel is the way to go. Just remember to hang on once the turbocharger spools, because you will be in for one wild ride. Diesel engines produce gobs of torque at low RPM, which pushes you back in your seat as the truck takes off when you start getting into the throttle.

Engine Longevity: Diesel engines operate at lower RPM and have much stronger engine parts than comparable gasoline engines. This translates into increased engine life, with diesel engines generally lasting up to 2x longer than gasoline engines before needing an overhaul or major repairs.

Cleaner Emissions: New technology has cleaned up the diesel combustion process, reducing the amount of harmful greenhouse emissions and virtually eliminating diesel soot from the exhaust.

Unlike petrol engines, there is no spark plug-in diesel engine. Ignition of the mixture is achieved by the pressure of air.

Functioning of the petrol engine

1. Suction stroke: When the piston comes down a low pressure is created in the upper part of the cylinder. This causes the inlet valve to open through which the mixture of petrol and air from the carburetor enter the cylinder.

2. Compression stroke: During the upward movement of the piston, the mixture gets compressed causing the inlet valve to close. The volume of the mixture drops to about one eighth of the original volume. Pressure and temperature of the mixture rise enormously.

3. Power stroke: As the piston gets to almost the last part of the upward stroke, the mixture is so highly compressed that its temperature and pressure reaches the maximum point. At the same time an electric spark at the top of the cylinder causes the mixture to ignite and explode. This piston is forced down within the cylinder. This movement is transmitted to the crankshaft through the piston rod. The crankshaft is attached to the car wheel. Hence the movement of the crankshaft is transmitted to the wheel of the car.

4. Exhaust stroke: As the piston comes down to the lower part of the cylinder the pressure inside the cylinder falls allowing the exhaust port to open. As the wheel makes the piston go upwards the waste mixture is discharged.

Functioning of the diesel engine

1. Suction stroke: As the piston comes down air is drawn into the cylinder.

2. Compression stroke:As the piston goes up the drawn air is compressed to high pressure and temperature.

3. Power stroke: At the end of the compression stroke, the air is compressed to the maximum increasing in its temperature and pressure. Now the fuel is injected into the air. Ignition takes place immediately causing the piston to go down. Its movement is transmitted to the crankshaft and to the flywheel and then to the car wheel.

4. Exhaust stroke:As the piston goes up to complete the cycle, the exhaust vapours are discharged out through the exhaust valve.

Advantages of Diesel Engine

It has higher torque
It gives higher power output
It is economical to use diesel as only 70% needs to be spent for fuel for getting the same mileage as a petrol car
Relaxed driving is ensured especially for long distances

Advantages of Petrol Engine
It is cheaper
Maintenance is easier
Engine noise is lesser

The choice between the two is dependent on individual requirements.

The main criteria of a car’s eco-friendliness is generally seen as the energy it uses in its operation. Cars have primarily run on oil-based fuel in the form of petrol or diesel for over a century. But we are now at the point where demand for oil is rising so much, and reserves are declining, that oil is actually running out. Oil prices have always been volatile and they react to speculation about events ranging from terrorism to hurricanes, but rising demand and diminishing reserves mean that overall, oil is just going to keep on getting more expensive. However despite this, most cars today still rely on oil as their primary source of energy; and oil is obviously a key contributor to carbon emissions, and climate change.

Petrol

Petrol has been the most popular fuel for cars in the UK for years; petrol engines are generally quiet and smooth, they are responsive and their performance is good. Petrol is currently slightly cheaper than diesel. Petrol engines emit around 10% more carbon dioxide (CO2) than diesel. However petrol cars pump out less toxic emissions than diesel. Unfortunately at the moment there is no single source of fuel which can compare with petroleum in terms of its instant bulk availability, energy density and (relative) cheapness.

Diesel

Diesel engines are more economical than petrol engines, therefore they emit less CO2. New ‘common rail’ diesels are approximately 10% more efficient than older diesels, and direct-injection diesel engines give the best fuel economy, diesels emit more particulates than petrol – but diesel engines with a particulate trap help prevent emissions of sooty particulates – ie. the clouds of smoke that you’ll experience if you follow old buses through towns. So diesel engines will generally provide you with more miles per gallon than their equivalent petrol models – just look at the differences between similar vehicles in our Green Car Guide. Diesel is currently more expensive to buy than petrol, and the forecasts are that diesel prices will continue to rise more steeply than petrol in the near future.

Diesel engines have always been seen as slow and noisy, however technology has seen some remarkable advances in recent years; for instance Honda has developed their own diesel engine that is designed to be quiet, refined, clean and with instant response – fighting against all the old stereotypes.

LPG

Over recent years, LPG (liquefied petroleum gas) has been a viable fuel option in the UK. LPG produces fewer emissions than petrol and diesel but fuel consumption is worse. It’s been possible to convert many existing cars to run on LPG by after-market conversions, and some manufacturers such as Vauxhall have had new cars in their range that are dual-fuel, which are designed to run primarily on LPG with petrol back-up. There is a reasonable network of filling stations.

LPG, and natural gas in heavier vehicles, has been an attractive proposition in the past primarily due to its cheaper cost, as it has enjoyed less fuel duty. However there is no guarantee that the Chancellor will maintain this in the future, and although there are some emissions improvements over petrol, LPG is still derived from a fossil fuel and therefore still releases greenhouse gases into the atmosphere.

CNG

Some vehicles, usually heavier vans or trucks that normally run on diesel, but also cars such as the Volvo (V70 Bi-Fuel), can run on CNG (Compressed Natural Gas), which again results in lower CO2 emissions than standard petrol cars, but the fuel is not as efficient as diesel. Finding CNG for refuelling can be a challenge.

Petrol-Electric Hybrids

Petrol-electric hybrid vehicles run on a combination of a conventional petrol engine and an electric motor powered by an energy storage device such as a battery pack. In simple terms they work on the principle that an electric motor provides the power at low speeds such as in urban driving, and they switch to petrol for driving at higher speeds. The batteries are recharged while driving and hybrids use regenerative braking, which means that energy is put back into the battery when braking, which improves energy efficiency.

Hybrid technologies improve fuel efficiency and therefore provide considerable fuel savings compared with a normal petrol vehicle – as well as carbon emissions savings. While models might cost more than conventional cars, running costs can be two-thirds that of equivalent petrol-fuelled vehicles.

Because of their lower CO2 emissions, hybrids also benefit from reduced vehicle excise duty and are treated favourably in Budgets. In addition they are exempted from the London Congestion Charge.

However at the moment there are a limited number of hybrid vehicle choices; there are currently just four hybrids available in the UK; the Toyota Prius, Honda Civic hybrid, Lexus RX400h and Lexus GS450h. As they are still a relatively new technology, there aren’t many available second-hand and so they are quite expensive.

Toyota’s first Prius (launched in Japan in 1997) didn’t sell in great numbers, however a new model has been introduced and this is now proving more successful. Although it looks like a normal car, it is designed around energy efficiency, and has many clever technological features that assist fuel consumption, including air conditioning and brakes powered by electricity rather than by sapping energy from the petrol engine. Lexus, part of Toyota, has introduced a hybrid version of the RX300, known as the RX400h. This is an SUV and because of its size, it still only returns around 35mpg compared to the Prius’s 65.7mpg.

An important technical issue of internal combustion engines is that a large part of the potential energy from the fuel is converted to heat in stead of useful power. And on top of that some of that power has to be used for cooling the engine to prevent overheating. The temperature of a running diesel engine is much lower than that of any other internal combustion engines, so a greater part of the energy from the fuel is converted into useful power and less of this power has to be used for cooling.

But that is only part of the reason of the efficiency of diesel. Another reason why these engines are more efficient is because the compression ratio. The compression ratio of a diesel engine is 14:1 up to 25:1 and the compression ratio of a gasoline engine is between 8:1 an 12:1. And the higher the compression ratio, the more efficient an engine will be.

Because of the efficiency the cost of using a diesel engine will be less than that of a gas engine. To be more specific: the fuel cost of a diesel generator per kilowatt is 30% to 50% lower compared to a gas generator.

And of course engines require maintenance. And that is yet another reason for the popularity of diesel engines: they require less maintenance and also last longer than gas engines. Partly this due to the lower temperature of the diesel engine we discussed before. But another reason is for the reliability and the lower maintenance cost is the fact that there are no spark plugs or spark wires in a diesel engine. So these parts cannot cause problems will not have to be replaced regularly.

The last prejudice I want to talk about is the fact that many people think that diesel engines are very noisy and smelly machines. And indeed that was true – in the past. But not any longer, because the past decades diesel technology has made great progress. Diesel engines run quieter and less noisy then ever. Better insulation material have been developed (and used). And also the use of mufflers has contributed to the low noise diesel engine.