Fuel economy in automobiles

The fuel consumption is the quantity of fuel that burns an internal combustion engine within a certain time or consumed by a vehicle in traversing a given route.

For road vehicles, the average fuel consumption is usually used at a distance of 100 kilometers as a benchmark in Europe. For other land vehicles and air and water vehicles and for drives are in liters per hour ( l / h ) or kilograms per hour spread (kg / h). For internal combustion engines, even the specific fuel consumption in grams per kilowatt-hour ( g / kWh) is an important parameter.

• 5.1 Calculation of CO2 emissions based on the fuel consumption
• 5.2 Conversion between l/100 km and mpg

• 6.1 car 6.1.1 Austria

Chemical relationships

The supplied energy in chemically bound form ( calorific value of the fuel or fuel ) is converted into mechanical work for driving / wave power in a combustion engine. However, the thermal efficiency only reflects the efficiency of energy conversion resist without quantitative information on supplied chemical energy and mechanical work performed to make. The non- extracted as mechanical work energy of the fuel usually goes largely lost as heat energy; Therefore, for example, serve to assess the fuel consumption of vehicles other specific, dependent on the use of reference variables ( distance traveled, time, passenger-kilometers, tonne-km, mechanical energy).

Consumption information for vehicles

Reference to the service transport work

In addition to the drive and the construction of the vehicle (weight, drag coefficient (Cd ), frontal area) and the logistics play a role for consumption. Transport can be better compared if the consumption is related to the transport work. Examples:

• Fuel consumption per passenger kilometer ( per person or seat and kilometers )
• Fuel consumption per freight ton (or cubic meters ) and kilometers

Here, the route makes the utilization of transportation, for aircraft a major role. Thus, the Lufthansa Group in 2010 consumed at 82 % occupancy average of 4.2 liters per 100 passenger kilometers, on flights of less than 800 km, there were an average of 7.5 liters per 100 passenger kilometers. Certain modern large aircraft came to a packed long-haul flights in 2003 with a fuel consumption of 2.7 liters per 100 passenger kilometers from. The same applies to other public transport such as railways, on average, more energy efficient though than some other motorized means of transport, but on branch lines has a higher energy consumption and final energy consumption per passenger kilometer because of low capacity utilization and high-speed services because of the air resistance of high-speed trains. Even when motorized transport, the vast majority of cars sold in Germany through the utilization plays an important role. Thus accounted for by the well 924 billion passenger kilometers, which were performed in Germany in 2008, only around 30 percent to passengers, at an average of just 1.5 people in the car, the utilization was only 30 %. In return, 44 billion liters of fuel were consumed, bringing 4.8l result per 100 passenger kilometers.

Compare by transport

• Train: about 2 liters per 100 passenger kilometers ( German track 52 grams of CO2 per passenger-kilometer, 0.20 kWh per passenger kilometer )
• Cars: 3-5 liters per 100 passenger kilometers (per vehicle 6-10 liters of petrol per 100 km, 185 g CO2/km; 0.60 kWh per passenger-km )
• Aircraft: about 3-8 liters per 100 passenger kilometers ( Lufthansa flights under 800 km 7.5 l, 2.7 l long-haul flights; 0.60 to 2.0 kWh per passenger-kilometer, as of 2012)

Specific consumption

In internal combustion engines typically the amount of fuel consumed is expressed per unit of labor, ie, the specific fuel consumption in g / kWh or kg / kWh. The indication in g / kWh is mainly for the optimal operating point, the operating point with the highest fuel efficiency. The actual specific consumption as a function of engine speed and power output is displayed in a consumption map production, whose graphical representation of a conch shell. Therefore, the consumption characteristic map is also referred to as shell chart.

In rocket engines, the specific fuel consumption is given as specific impulse.

Reference to the calorific value

In power plants, the amount of time spent per propellant or fuel, although logistically interesting, but their efficiency is indicated by the amount of energy converted per calorific value of the fuel. Modern gas -steam combined cycle power plants can convert up to 60 % of the heating value in electric power, coal-fired power plants and diesel generators, this value is about 40 %.

Conversions

Calculation of CO2 emissions based on the fuel consumption

When discussing the greenhouse effect of carbon dioxide fraction ( CO2) is valued on the exhaust gases. An ideal in this sense fuel is hydrogen. He is completely converted to water. The other extreme is pure carbon (coal), it burns completely to carbon dioxide (CO2). Common fuels consist primarily of hydrocarbons and in between (hydrogen is mainly produced from hydrocarbons, carbon dioxide is then also free; see main article hydrogen). The carbon content of fuel is constant and a carbon atom with two oxygen atoms forms a CO2 molecule. Other compounds hardly form. Therefore, the consumption can be directly the amount of CO2 produced calculated by 32 grams of oxygen are added according to the molar mass of 12 g carbon.

During the combustion of produced

In addition to water and small quantities of other products of combustion from the combustion of

During the combustion of one liter diesel represents about 14% more CO2 than burning a liter of gasoline, that is, if a gasoline engine has a fuel consumption by about 14 % compared to a diesel engine is produced, the motors are equivalent in terms of CO2 emissions. Therefore, gasoline and diesel vehicles can not be measured easily on the fuel consumption in liters compared. This is caused by differences in specific gravity (density of diesel about 12% higher) and the ratio between carbon and hydrogen atoms in the molecules of the two.

The proposed by the European Commission for cars guideline of 130 g CO2 per km corresponds to a consumption of 5.0 l/100 km and 5.6 l/100 km diesel fuel. The entering into force in 2012 EU emissions law prescribes a fleet emissions of 120 g CO2/km.

Conversion of motor vehicles of consumption data given in [ l/100 km] in [g / km CO2]: Calculation example for a petrol engine with 5.6 l/100 km Fuel consumption:

5.6 l/100 km * 2.32 kg CO2 / l = 12.992 kg CO2 / 100 km = 129.92 g CO2/km

It is about 100 km averaged values ​​. Routes uphill increase the emissions drastically while driving downhill cause kilometer- related emissions for motor fuel cut.

Conversion between l/100 km and mpg

In Imperial measurement of the fuel consumption of vehicles in miles per gallon is given. The abbreviation is: mpg or MPG. The unit mpg refers to the distance traveled in miles ( 1.6093 km ), for a gallon of fuel is consumed. In some African countries, Japan and South America, and partly in the Netherlands, the unit kilometers per liter is in use.

The Anglo-American unit volume gallon is not uniquely determined. In the U.S., it corresponds to 3.785 liters, in the UK, however, 4,546 liters. Therefore, a distinction is made between mpg (U.S.) and mpg (UK).

Motor vehicles

Car

For motor vehicles, the fuel consumption is usually gem in liters per 100 km driving distance for the standardized driving cycle in Europe. 70/220/EEC specified. It represents mainly a comparison of vehicles through consistent measurement; a statement about the actual consumption of a vehicle type in everyday driving is secondary. It is therefore not very informative with respect to the assessment of the economy and the level of CO2 emissions from automobiles. The value is determined by the vehicle completed a specified driving cycle provided and the amount of fuel consumed is measured. Critics complain that to determine the data experienced drivers would be used to achieve the lowest possible consumption within specification.

In order to establish uniform boundary conditions, the calculation of fuel consumption takes place since 1 January 1996 generally on a chassis dynamometer.

The standardized driving cycles are average profiles; they make the vehicles compared with each other, but do not agree with the usage profile of each customer, especially not with the profile of customers who drive little foresight (frequent acceleration and braking ), which in a high proportion of their route short-distance and urban transport cover and / or driving on motorways very high speeds.

Widespread driving cycles are:

• In the European Union is the fuel consumption of motor vehicles based on the NEDC (New European Driving Cycle) in accordance with Directive 80/1268/EWG Annex I, Licensed changed determined by 93/116/EC. Here, a synthetic cycle is used with clearly defined acceleration, constant velocity and deceleration phases on a test stand. For vehicles with manual transmission, also the driven gears are required.
• The U.S. FTP75 is a cycle, which is the figure a study carried out on the public roads driving.
• In Japan, the so-called 10-15 mode is used. He is (like the NEDC), a synthetic cycle, but has a different course.

The resulting through the various cycles consumption differ greatly in part and are therefore not directly comparable. Technical measures of car manufacturers to reduce fuel consumption relate to more efficient engines, reducing the air resistance and the rolling resistance of the tires as well as alternative drive concepts. As newer generations of vehicles fail usually wider and higher, to improve the air resistance by the value is opposed by the increase of the end face. In addition to above all the use of it ( " energy-saving driving style " ) to reduce energy consumption greatly.

Sometimes referred to the motor power consumption is specified in order to propagate the supposed efficiency of a powerful engine. To this end, for example, determined in the NEDC fuel consumption divided by the rated power. This marketing statement (see also greenwashing ) can not be used for an objective comparison because consumption occurs at maximum power, which are far beyond the determined in the driving cycles values ​​and no direct relationship between the rated power of an engine and the consumption in a standard cycle there.

Austria

In Austria in car sales brochures, advertisements and posters of traders have information on fuel economy in a many years - must be minimum font size - relatively small. In the beginning, data for speed of 90 km / h and 120 km / h and Urban Transport usual, and later a " of thirds " of it. Since 2010, the figures are based on urban and rural transport and a weighted 1:2 means it.

Trucks and buses

Since trucks and buses can be represented only bad about the current NEDC for cars, they are subject to other conditions which 70030 (Part 2) are written in DIN.

These vehicles according to DIN 70010 ( which also include trucks and buses ) are ( tire pressure, ...) to assemble in the measurement using a standard lubricants and operating parameters. The vehicle weight is the average weight (average of the maximum permissible and empty weight).

Also to the ambient conditions stringent requirements are imposed. So must dry and calm weather a certain temperature and a certain air pressure prevail.

The test speed shall be 75 % of the vehicle speed.

To compensate for uncertainties, the spent fuel is a test surface to height by 10%.

Manufacturer's data on fuel consumption

The determination of the manufacturer will invariably take on dynamometers and in accordance with European standard driving cycles ( NEDC), which is intended to reflect a ride in a European city and on country roads. The vehicle must have a certain loading condition and above all the standard equipment. The average consumption values ​​that are displayed in the vehicle using an onboard computer, often differ by up to 10 % off the top or bottom of the actual fuel consumption. Reasons for this are, among others, the strong variation of Radabrollumfängen that mounted by different dimensions wheels ( summer or winter tires) or be caused by reduced tread depth.

The actual consumption is strongly influenced by driving style of the driver and other environmental conditions such as weather, road conditions, etc. depending. Contrary to some opinions, it is quite possible to undercut the determined consumption figures yet. Particularly large-volume engines in conjunction with manual transmissions are forced in the NEDC to unfavorable operating points.

After an analysis of the International Council on Clean Transportation, the real consumption in 2001 was 10%, in 2011 25% higher than the official manufacturer's instructions. The Auto Club Europa came in 2012 to an average of 19.6% higher consumption.

Particularly high, the difference between real practice consumption and the manufacturer's instructions fail in hybrid vehicles. An example of this route profiles with long interests in motorway journeys where the braking action and therefore the energy recovery is very low. Another reason for the deviation is to be sought in the different boundary conditions between the measurements on the test bench role and the real customer profile.

Since the publication requirement leads to comparability and the purchasing decisions influenced by the automobile manufacturers strive to publish the best possible values ​​. To this end, all actions are taken that affect the outcome positive. In the course of this complaint against the producers again and again unrealistic or even the standard specifications use conflicting measures. These include, for example:

• Use of particularly low rolling resistance, filled with high pressure air special tires (usually very small and narrow, the air pressure must still be within the manufacturer's instructions and the tires must be approved for sale in the market freely and the vehicle type )
• Use of special lubricants that reduce the energy loss due to friction ( also within the approved by the manufacturers oil types)
• Shutdown of energy consumers
• Correction of the track ( can increase wear and / or safety deteriorate)
• Lightweight as possible by removing unnecessary accessories ( spare tire, tool kit, etc.)
• Measurement in the basic version with no optional equipment
• Optimized mode, when the vehicle control unit to recognize that a test is performed on a chassis dynamometer
• Disconnecting the alternator by the control unit, so that no fuel consumption for charging the battery is obtained
• Reduce vehicle weight by specific equipment
• Door slots and grille are glued in order to achieve better aerodynamics
• Selection of an Outstanding vehicle from the production