In the early stages of the automobile, there was only one priority: High driving performance. Fuel consumption was, initially, a minor matter. Therefore the first attempts to reduce the consumption of petrol emerged in the 1950s. First, the car model Gutbrod Superior 700 E came into the picture, which received a direct petrol injector built into the two-stroke engine by former aircraft engine constructor Hans Scherenberg. A short time later another car, the Goliath 700 GP, was also driving the streets with this technology.What does that mean exactly?The difference between the injector types built into those cars is evident in the terms themselves: As opposed to the conventional injection for Otto engines, where the injection valve is located in the inlet manifold in front of the intake valve, direct injection involves injection directly into the cylinder.
And, as is so often the case in life, the direct route is the best: This technology, developed for aircraft construction, resulted in a saving of 30 percent.

The first “baby steps" with regard to this technology, however, occurred already earlier. As a pioneer, BMW conducted the first trials with the BMW VI, a four-stroke, twelve-cylinder engine. The technology worked so well that in the 1930s, Mercedes-Benz implemented it in supercharged four-stroke aircraft engines. Almost two decades later, in 1954, Mercedes-Benz also delivered for cars: The high performance engine of the 300 SL was also temporarily equipped with petrol direct injection. Three years later however, in 1957, the change was made back to inlet manifold injection, because the direct injection procedure caused problems through the thinning of oil. The revival of this technology however came ten years later when, in 1967, Volkswagen also experimented with direct injection technology: The Volkswagen 1600 TL for the first time received electronically controlled petrol injection. Since then, engineers have been ardently exploring the combustion process in the motor, in order to improve efficiency internally, eg. with modifications to the piston crown and pistons.
But as usual there are different ways to reach the goal: An alternative fuel saving concept was brought to the public in 1964, when the Auto Union introduced the Audi 72 to the market, with a medium pressure motor. The piston crown in this motor contained a spherical combustion chamber, which lead to improved combustion. Many modifications were to follow, including, among others, the electronic throttle control from BMW at the end of the 1990s.
Another steppingstone in the right direction was reached as early as 1947, when the American Ralph Miller received a patent for his overlapping valve timing design. The new thing about this was that the inlet valve remained open at the beginning of the compression process. Thus, a small amount of air-fuel mixture was expelled, which would then be immediately available for the following intake stroke without delay. Honda, Toyota and BMW developed this concept further in introducing intelligent valve control to their motors, which provided for different valve opening times for different driving conditions. In the 1980s, Cadillac equipped its eight-cylinder engines with a cylinder cut-off. Four, six or eight cylinders were in operation at any one time, depending on power requirements. This also led to a saving in fuel.A further development was the lean burn motor, first introduced by Toyota in 1991. Here, the fuel-air mixture was kept extremely lean (that is, with an excess air ratio of 1:21), which led to reductions in consumption, but also entailed disadvantages in starting. The lean burn mixture could only be realised in certain rpm ranges, and the unsatisfactory results lead to the abandonment of the lean burn principle.
In 1997 Mitsubishi went back to the roots of direct fuel injection by presenting the Charisma GDi (Gasoline Direct Injection), the first mass-produced vehicle with petrol direct injection. Volkswagen followed with the FSI motor in 2000. Meanwhile, more and more manufacturers are using this technology – especially in connection with turbocharging and/or supercharging, with which the fundamental torque weakness of petrol direct injection can be remedied. The real success of direct injection in automobile construction, however, began with the advanced development of the diesel engine. The Volkswagen Golf Diesel revolutionised the market in 1976 with the first fast-running diesel engine with a 1.5 litre motor (37 kW/50 hp). This engine accelerated the compact vehicle to 140 km/h, at what was at the time an amazing consumption of 6.5 l/100 km – with a little bit of restraint, less than five litres was also possible. A further advance in development was brought about by the introduction of turbo diesel direct injection, which has presented at the IAA in 1999 by Volkswagen subsidiary Audi. Here, also, the fuel is injected directly into the cylinder, which means that the prechamber or swirl chamber otherwise customary in diesel motors can be foregone. The advantage of direct injection is its efficiency, however in the early stages of development the price of this was loud combustion noise. The motor of the first Audi 100 TDI series had five cylinders, supplied 88 kW (120 hp) and could be driven with consumption figures between six and seven litres. Previously, Fiat had already introduced common rail direct injection, developed in cooperation with Bosch, in the Croma. The common rail motors are now considered to be gentle bruisers.

Currently, engineers in the automobile industry are working on the combination of diesel and Otto engines. Accordingly, with the “Diesotto” Daimler Benz presents a 1.8 litre petrol engine which is compressed to a similar level to a diesel, and for which the premium fuel is ignited automatically in some rpm ranges, as in a diesel. Synthetic fuels and complex emission controls, eg. with the injection of urea by the Mercedes “Bluetec” models, should however make the diesel a sustainable option for the future.One current trend of motor development is downsizing – a reduction in engine size, which generally leads to a reduction in consumption. The loss of power is compensated for by the supercharging or turbocharging. As such, with the 1.4 TSI Volkswagen introduced a 1.4 litre petrol direct injection engine, which is inspired with a supercharger and a turbocharger. The result is a full 125 kW (170 hp), which results in on average 7.3 litres of premium fuel (174g CO2 per kilometre) for the Golf. With this, Volkswagen currently represents the spearhead of the new technology.Nowadays modern petrol direct injection engines use piezo technology. For diesel engines, direct injection with fast piezo injectors has led to noticeable fuel savings. In August, 2006, this technology was also used in an Otto engine for the first time, that of the Mercedes-Benz CLS 350 CGI. The advantage of piezo injectors: They inject the fuel into the combustion chamber so finely that it can be ignited immediately, and without mixing with air. The petrol can thus be used more efficiently. At the same time, constructors from Bosch, the specialists for injector pumps, are working on the development of petrol direct injection with magnetically controlled injector valves. The second generation of this technology also comes onto the market in 2007, and will premiere in a turbocharged 1.6 litre Otto engine developed cooperatively by BMW and PSA for the Mini Cooper S, among others.Automobile engineers see further potential savings in refining aerodynamics, and in the implementation of supporting units of a vehicle such as water pumps, hydraulic pumps, air-conditioner compressors and so forth, according to requirements. However, the selection of the “correct tyres optimised for minimum road resistance”, auto start/stop function and brake energy regeneration system also help to achieve significant savings. BMW is the most dedicated in this regard, and presents an entire bundle of these measures in its new EfficientDynamics models
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All roads lead to Rome but Rome wasn't build in a day - in the context of fuel saving concepts it translates into a series of different strategies to make the car more environmentally friendly. Here is a brief overview of what's happening in the marketplace:
Audi Ultra Low Emission SystemThis term is used by Audi to describe a program in which the consumption, and consequently the CO2 emissions, of all its models are to be reduced by 20% by the year 2012. Audi will commence this program in 2008 with the three litre TDO-V6 in the Q7 and A4. Other models with TDI and TFSI engines should follow soon after. The consumption-reducing technologies of the modular efficiency kits, and the TDI motors with the “ultra low emission system”, are the central focus of the strategy. A kit with hybrid modules for various vehicle models completes the efficiency strategy.
BMWBMW began to develop motors which operated especially economically at an early stage. At the beginning of the 1960s, BMW built its “new class”, the 1500/1800/2000 motors, which were especially powerful and also handled fuel quite economically – the success of careful engine construction. Here, the most modern construction formulas were used: Overhead camshaft, floating valves, carefully designed combustion chambers, smoothly polished inlet ports. Things that are taken for granted today, but which were certainly not in previous years. Quite early, namely at the beginning of the 1970s, BMW introduced petrol injection first in the 2002 tii, and later in the 3-series and 5-series. BMW engineers were quick to recognise that an engine with a lower rate of revolutions would consume less fuel: They brought the 525e into the program, a middle-class vehicle with long transmission ratio and large engine. “Downsizing” was also observed from early on: The new 7-series luxury class contained the 745i, a model with a 3.6 litre six-cylinder engine which, thanks to a turbocharger, had the power of a 4.5 litre engine. In 1986, four-valve technology also appeared in an engine in BMW colours, which also contributed to economy. In 1995, alongside Ford and Volvo, BMW was among the first brands in Germany to offer customers bivalent natural gas engines.

In the middle of the 1990s, the electronic throttle control was invented at BMW and filed as a patent. It ensured that the motor was fed an even more carefully prepared petrol-air mixture. It made BMW engines around ten percent more economical than was previously the case. New BMW models use EfficientDynamics – the most state of the art strategy for the preservation of resources. BMW uses this term to combine various technical innovations which produce reduced consumption at increased power. This includes brake energy regeneration to charge the battery, electronic steering assistance, a shift point indicator (only for manual models) and the auto start/stop function (118i/d and 120i/d). Furthermore, both 2.0 litre four-cylinder petrol engines (118i and 120i) will be changed over to High Precision Injection (direct injection with lean operation). The diesel models will be equipped with a particle filter as standard. The BMW 123d is evidence of what all this can achieve, as a sports car with 150 kW (204 hp) which is satisfied with an average of 5.2 litres of diesel (138g CO2/km). The four-cylinder engine has a two-stage turbocharger, referred to by BMW as Variable Twin Turbo (VTT).
Mercedes BenzThe Mercedes-Benz “DiesOtto” concept endeavours to make a petrol engine as efficient as a diesel engine. Mercedes-Benz plans a 1.8 litre four-cylinder unit, which combines the strengths of the low-emission Otto engine with the consumption advantages of the diesel motor. The “downsizing”, the reduction of engine size at high engine performance, is a substantial factor in the reduction of consumption. A vehicle in the luxury class with 175 kW (238 hp) and 400 Nm of torque, together with a hybrid component, require less than 6.0 l/100 km.The DiesOtto, according to Mercedes, functions as a self-igniting engine in the part load operational range, while the mixture is ignited by spark plugs when under full power, as is the case for conventional petrol engines. In order to be able to realise the two different combustion principles, the motor must operate with a variable combustion ratio. This is due to the higher pressure necessary for the self-ignition in the part load operational area. This is effected with a variable crank gear – the stroke, that is, the path travelled by the piston, is thereby altered. A fully variable valve control is also present in the form of Valvetronic, as has been standard for BMW for a few years.
GM HCCI-SystemGeneral Motors brought two experimental vehicles to the streets for summer, 2007. These are, for the first time, equipped with a new combustion technology in a 2.2 litre Ecotec engine with central direct injection, variable valve control and two electronically adjustable camshafts. This combustion technology is called Homogenous Charge Compression Ignition (HCCI). When combined with other measures, the HCCI vehicles should reduce fuel consumption by up to fifteen percent, and already satisfy future emissions standards today. An HCCI motor offers up to 80 percent of the fuel efficiency of a diesel engine, without, however, the necessity of the expensive aftertreatment of nitric oxide. These increases in efficiency result, primarily, from the fact that the petrol is ignited at a lower temperature, and thus less energy is lost in the form of heat. CO2 emissions are reduced commensurately with the fuel consumption.Heat is required for the operation of the HCCI process. In order to quickly generate this heat in the cylinders after a cold start, the motor is initially run using conventional ignition. In HCCI mode, the fuel-air mixture is comparatively lean, that is, the air component is particularly high. The system thereby offers roughly the same efficiency as a diesel, which can be up to 25 percent better than that of a conventional petrol engine.
"Opel ecoFlex"The premiere model for the Opel ecoFlex series is a Corsa 1.3 CDTI. This will consume approx. 4.5 l/100 km (119g CO2/km), and should be available in 2008. ecoFlex is Opel‘s future label for vehicles in their series which combine low consumption, low emissions and operating efficiency. Conventional combustion engines are becoming more efficient and economical through technical measures. Eco-Turbo and CNG (Compressed Natural Gas) are the names of motor concepts upon which the ecoFlex models are based. Eco-Turbo is a downsizing concept which involves the replacement of large motors with smaller supercharged units. An example is the Opel Astra 2.0l Turbo (125 kW/170 hp), which has been replaced by a 1.6 l Turbo ECOTEC (132 kW/180 hp), the result of which was a reduction in consumption of approx. fourteen percent. A series of other technical measures accompany and support the objective of making this vehicle yet more efficient and cleaner.
PEUGEOTThe particle filter system (FAP) has played a substantial role in Peugeot’s long-term active environmental strategy since 2001. In combining FAP and modern common rail direct diesel injection, the engines are not merely more economical, but also emit fewer particles. In addition, Peugeot also emphasises the downsizing principle.RENAULTThe new 1.2 l 16V TCE (74 kW/100 hp) is a current example of the success of downsizing at Renault. It provides the same power as its 1.4 l predecessor, and at 145 Nm the torque of a conventional 1.6 l engine. The motor, however, has an average consumption of 5.9 l of premium fuel (140g CO2/km).
Smart: “smart fortwo cdi“One of the smallest diesel direct injection engines with a turbocharger in the world is built into the smart fortwo cdi. The 0.8 l diesel engine (33 kW/45 hp) has torque of 110 Nm. The small two-seater uses 3.3 l/100 km, and 88g CO2/km. When combined with the start/stop technology now on offer, smart refers to a Micro Hybrid System.
VolkswagenFundamentally, in the area of petrol engines (TSI) and diesel engines (TDI), Volkswagen is going the way of highly supercharged motors with the combination of turbocharger and supercharger. With direct injection and smaller engines, Volkswagen obtains comparatively high power with low consumption. The 1.4 l TSI engines already comprise three power levels: 90 kW/122 hp, 103 kW/140 hp and 125 kW/170 hp. These engines are even more economical when driven in combination with the automated dual clutch gearbox, “DSG”, than when driven manually. In vehicles with DSG, which allow the vehicle to be driven as if it were an automatic gearbox, lower consumption figures are achieved than for a manual vehicle. The 1.4 litre/170 hp TSI averages only 7.5 l/100 km according to EU standards. Volkswagen is conducting intensive research on self-igniting Otto engines, the Gasoline Compression Ignition System, which functions in a similar way to the DiesOtto engine from Mercedes. Testing vehicles with the GCI motor were presented to the public at the end of 2006. In the area of diesel engines, Volkswagen sees advantages in the Combined Combustion System (CCS), which combines the advantages of the self-igniting, economical diesel motor with the advantages of the low-emissions petrol engine in one unit. This, however, requires a new type of synthetic fuel source.