The term low-energy vehicle (NEF) refers to vehicles that realize significantly reduced fuel consumption (below 0.58 kwh/km or 1.8 MJ/km) compared to current average fleet consumption. However, the upstream primary energy input required for this must be included in the balance sheet. D. H. Z. B. The energy used before the energy is in the battery, the energy used to produce it, and the energy used to dispose of or recycle it. The concept is based on the low-energy house. A standard does not yet exist. However, there are already different tax classifications (z. B. Temporary tax exemption for the three-liter car). More specific terms are one-liter car, two-liter car, three-lane car and five-liter car.
Table of Contents
motivation
Economy
The need to produce and operate vehicles with the lowest possible fuel consumption results from the constraints of energy conservation. In addition to the sustainable use of limited energy resources, what counts most is the economical operation of the vehicles. In addition to the purchase costs, the steady rise in fuel prices and the political, i.e. fiscal, promotion of fuel-efficient vehicles against the background of the increase in the number of vehicle registrations worldwide have a major influence on the economic viability of these vehicles.
a major boost to the construction of low-energy vehicles came with the announcement by the california government that, from a start date (postponed several times), it would impose punitive taxes on all manufacturers who did not produce a certain proportion of their vehicles in accordance with the ULEV (ultra low emission vehicle) or. Produce ZEV (zero emission vehicle) principle. ZEV means that the vehicle must be able to cover a certain distance completely without emissions. today, this capability can be provided virtually only by electrically powered vehicles – the main driving force behind the hybrid efforts of the major automakers. In europe, the EEV standard (enhanced environmentally friendly vehicle) is a motivating factor.
As early as 1996, the german manufacturer audi introduced an audi 100 duo, which was soon discontinued due to lack of demand (and the simple and inefficient technology). The German three-liter models audi A2 TDI 3 l and VW lupo TDI 3 l also failed to generate an economic return – despite tax incentives for sales and subsidies for development – and the VW Group subsequently discontinued production.
Environmental protection
Car combustion engines are responsible for about 20 percent of the world’s CO2 emissions, which are a major contributor to global warming. Furthermore, petroleum reserves, which serve as the energy source for most of today’s motor vehicles, are expected to become increasingly scarce in the coming decades (see global peak oil production). the motivation is the ALARA principle (as low as reasonably acceptable – as low as reasonably bearable) or. Generally an ethical behavior. This ethical behavior can at least be attributed to some so-called "garage companies" that – often with roots in the ecological movement – produce vehicles based on bicycle technology in very small series and, for example, are also concerned about the environmentally friendly generation of the energy required for propulsion.
the verkehrsclub deutschland publishes the auto-environment list, which is based, among other things, on energy consumption. Another rating is the FIA ecotest.
Specification of energy consumption
In europe, fuel consumption for motor vehicles is usually expressed in liters of fuel per 100 km driven (distance consumed). In order to arrive at comparable figures, the energy content of different fuels must be taken into account. Diesel fuel has an energy density of 9.8 kwh/l, gasoline 8.9 kwh/l. Both have a mass-related energy density of about 12 kwh/kg, natural gas 14-15 kwh/kg.
Another way to measure energy consumption is in terms of the amount of energy used per payload transported per trip. This is the distance consumption per weight [l/(100 km*100 kg)]. comparing a truck carrying 20 tons of freight with 35 liters of diesel over 100 km with a fully loaded diesel car carrying 500 kg of freight (passengers+luggage) with 7.5 l, the energy consumption of the truck is 0.175 l/100 kg, while the car needs 8.5 times as much, i.e. 1.5 l for 100 kg per 100 km.
However, such a consideration neglects the driving time and thus the driving resistance, which increases with increasing speed. However, only transport performance at the same speed can be compared, d. H. The distance consumption per weight and time [l/(kg*km*h)]. A "3-liter car" loaded with 500 kg has z. B. At 85 km/h (speed comparable to that of a truck), the distance consumed is approx. 2 l/100 km (mid-size car ca. 4l/100 km) and thus a distance consumption per weight of 0.4 l/(100 kg*100 km). The higher fuel consumption of the car compared with the truck is mainly due to the less favorable operating point of the car engine at 85 km/h, since the car engine is much further away from full load at 85 km/h than the truck engine (s.U.). With a smaller engine, the car could achieve similar efficiency – but with similar mileage.
The energy consumption labeling ordinance, known as CO2 labeling for short, does not address the energy consumption per km in joule or kwh.
Design measures to save fuel
The energy consumption of a vehicle depends not only on its design but also on the way it is used. How to reduce consumption even further by driving in an energy-saving manner.The distance consumption [l/100 km] of a passenger car is mainly determined by (1) the driving resistance and (2) the efficiency.
- Driving resistances: the driving resistance determines the necessary drive power [kw] to achieve the desired driving performance (acceleration, top speed). At constant speeds, rolling resistance, which is directly proportional to speed, predominates; as speed increases, flow resistance (air resistance), which is quadratically proportional to speed, predominates. The acceleration resistance is v. A. Significant in urban traffic.
: the acceleration resistance occurs when the speed changes. It is directly proportional to the vehicle mass. Lightweight cars allow the use of smaller engines at the same acceleration, which operate at a more efficient operating point at constant speed (where rolling resistance and aerodynamic drag are significant). Negative acceleration resistance (during braking) can be used for energy recovery (recuperation). Low rolling resistance coefficient due to low rolling resistance tires, low vehicle weight, low-friction wheel bearings. (flow resistance):
- Reducing the drag coefficient by means of a streamlined body shape, clad wheel arches and smooth surfaces (cw value up to approx. 0.16), narrow tires, no door buckles, camera instead of side mirrors.
- Reduction of the cross-sectional area of the vehicle exposed to the air flow (vehicle projection area) due to seats arranged one behind the other or at least offset (two-seater with approx. 1 m² of vehicle projection area), or low seating position and little overhead space.
- The efficiency describes the efficiency of the conversion of z. B. chemical or electrical power into mechanical power: the main problem of the internal combustion engine is that its efficiency is highest at full load and decreases towards low loads. Specific consumption [g/kwh] therefore increases sharply as the engine load decreases. There are two approaches to solving this problem:
- Efficiency-optimal gear ratio: power is the product of speed and torque. In order to produce a certain power, the most efficient operating point is the one at which this power is achieved with maximum load and lowest possible engine speed.
- In manual transmissions, "long gear ratios a simple means. The gearbox efficiency itself is close to 100%. However, the low acceleration reserve ("elasticity") in such a drive stage reduces the acceptance. Are an alternative to always driving the engine with high loads, but they have so far been used with only approx. 90% worse efficiency than manual transmissions and are not particularly accepted (there is no direct relationship between speed and engine speed).
- In principle, diesel engines are more efficient than gasoline engines due to the lack of throttle losses in the part-load range. In diesel engines, the lack of knocking tendency of the fuel allows high supercharging at a high compression ratio with a simultaneously low injected fuel quantity. As a result, the engine is operated in lean-burn mode, which also significantly increases efficiency. However, the emission of nox increases, which makes it problematic to achieve high emission standards.
- Electric motors have a much higher efficiency in the part-load range than internal combustion engines.
- The hybrid drive reduces the problem of high specific consumption of the combustion engines in the part-load range, since an additional electric motor operates at low loads, while the combustion engine is used only at higher loads.
- Also by charging, z. B. turbocharging or compressors, the efficiency of an engine can be significantly increased in the part-load range. The liter output is significantly increased so that the desired nominal output is achieved with lower stroke volumes. As a result, the engine operates at higher – and thus more efficient – load points in the part-load range (downsizing).
- For gasoline engines, lean-burn operation also improves efficiency at partial load, but is problematic from the point of view of pollutant emissions (nox). lean-burn engines, z. B. Gasoline direct-injection engines with stratified charge operation therefore require complex exhaust gas aftertreatment, such as nox storage catalytic converters.
- The efficiency of internal combustion engines can also be increased in the part-load range by cylinder deactivation (ZAS). At low loads, cylinders are switched off, resulting in a higher and thus more efficient load point for the working cylinders. With small engines, however, the ZAS leads to a deterioration in noise comfort, which is not accepted.
Vehicle design
First of all, the driving resistance must be kept as low as possible in accordance with the purpose of use.
- Passenger cars for urban traffic should have the lowest possible acceleration resistance (low vehicle mass) and, where appropriate. Have recuperation. your rolling resistance should be low (low vehicle mass). The flow resistance (air resistance) does not play such a big role here. Example: "smart.
- Passenger cars for intercity traffic should above all have the lowest possible flow resistance (air resistance), d.H. A small vehicle projection area and a low cw value. Example: "cabin scooter" type, loremo, 1-liter car from VW.
In the second step, the engine should be designed so that it has the highest possible efficiency under all typical operating conditions.
- In the case of the electric motor, the efficiency is largely independent of the operating condition.
- Internal combustion engines should always be operated with the highest possible load. Oversized internal combustion engines are more problematic in principle from the point of view of the most favorable operating point possible, since they are more expensive in "everyday use" often operate at low – and thus inefficient – load points. However, this problem can be solved with an efficiency-optimized gear ratio (s.O.) quite solvable.
Classification of NEF
In germany, some vehicles with particularly favorable fuel consumption values enjoyed tax concessions. However, vehicles are not classified according to their energy consumption, but according to their carbon dioxide emissions, measured in accordance with Directive 93/116/EC.
According to German tax law, a five-liter car less than 120 g CO2/km. This corresponds to a distance consumption of 5.06 l/100 km gasoline or 4.53 l/100 km diesel. If the engine is approved before 1. January 2000 these vehicles were exempt from vehicle tax. The term three-liter car is associated with a carbon dioxide emission of 90 g CO2/km for tax purposes. This corresponds to a distance consumption of around 3.4 l/100 km diesel or 3.8 l/100 km gasoline. The same rules apply to alternative fuels in internal combustion engines, electric vehicles are taxed according to vehicle mass.
The term one-liter car means vehicles with a fuel consumption of less than 1.5 l/100 km, although for marketing reasons, vehicles with a fuel consumption of 1.5-1.99 l/100 km are often also placed in this category.
models
Ultimately, the permanent introduction of such vehicles on a broad front has failed so far. However, some of the technology has found its way into the series production of "normal" passenger cars (electrohydraulic clutch, covered hubcaps).
Models such as the smart show that even the smallest vehicles are accepted by buyers. Medium-sized vehicles from some manufacturers achieve fleet consumption of 7.5 liters, which, according to some, makes it advisable for the state to take legal action (as in California) to demand a reduction in these values.
Series models
Consumption of some series models (selection):
<52 g/km (electricity mix germany)
Production model in preparation
: probably in 2010, the 2-liter diesel car of the munich company loremo (no test standard specification) should be available at a price of less than 15.000 euro, reach a top speed of 160 km/h, be designed for 2+2 people and have a range of 1300 km. An electric version is also planned.
- Aptera type-1: production start expected in october 2008, sales initially in california only. There is a hybrid version with a gasoline engine and a purely electric version. The cd value of the two-seater, three-wheeled vehicle is 0.11. The hybrid version has an average consumption of 1 l/100 km.
Studies
- The citroen ECO 2000 SL 10, developed between 1981 and 1984, achieved a total consumption of 3.5 liters of gasoline per 100 km. Features of the study were applied in the development of the citroen AX. [1]
- the mitsubishi "i" concept [2] achieved only 3.8 l/100 km in the FIA ecotest 2003, but this was under practical conditions such as operation on a freeway and with air conditioning. [3] the most economical competitors in the test (audi A2 1.4 TDI, mini one 1.6, suzuki ignis 1.3 ddis) achieved 4.5 l/100 km under these conditions. [4] the opel corsa ECO 3 l consumed 4.3-4.7 l/100 km in practice.
- The twingo smile from greenpeace consumed 3.5 l of gasoline (RL93/116/EWG). [5]
- the VW 1-liter car is a study so far. According to VW, the development, which was halted at the time due to excessive costs, was resumed because of significantly reduced costs. It is to be built in series from 2010. [1]
- The bionic car is a concept study presented by mercedes-benz in 2005. The suitcase fish served as the aerodynamic model for the development of the vehicle. The fuel consumption of the diesel-powered four-seater with a cd value of 0.19 is expected to be 4.3 l/100 km. [6]
- The jetcar (two-seater) consumes 2.9 l diesel per 100 km. (no standard consumption, determined on a test drive by the manufacturer’s employees – with TuV report). [7]
- The concept study of the toyotas ES3 with diesel hybrid drive achieved 2.7 l/100 km (87 mpg). [8]
[opensourcecar]: [9] development of a 2-passenger electric car by students of the TU darmstadt, 6 kwh/100 km, range 300 km, top speed 130 km/h
- The daihatsu UFE III has a combined fuel consumption of 2.1 l/100 km [10]
Electric vehicles
In addition to vehicles with internal combustion engines, electric vehicles also achieve final energy consumptions equivalent to one liter of diesel per 100 km (which is approx. 10 kwh/100 km), in some cases even below. These are, for example, vehicles with lightweight bodies such as the hotzenblitz, whose production has since been discontinued, and the kewet from norway. The most economical car is probably the two-seater TWIKE, which regularly needs less than 5 kwh per 100 km off the grid (measured). This is roughly equivalent to a 0.5 liter car. The "only" single-seater cityel needs similarly little. Even vehicles with a normal small car body like the citroen AX electrique consume the equivalent of significantly less than 2 l/100 km. According to long-term consumption measurements, the citroen AX electrique runs on around 15 kWh per 100 km, measured from the power socket, i.e. including all charging and battery losses. Based on 308 g CO2 per kWh (published for the EON electricity mix in Bavaria in mid-2007), this results in CO2 emissions of around 46 g CO2 per km when supplied with the normal electricity mix (however, this calculation does not take into account the line losses from the power plant to the socket and transformer losses). If the batteries are recharged with CO2-free solar, wind or hydroelectric power, the CO2 impact per km is even lower and tends toward zero. There are also vehicles that consume even less through consistent optimization.
Other vehicles: cityel, TWIKE, these vehicles consume the equivalent of less than 1 l/100 km. The tesla roadster from tesla motors (california) with purely electric drive and driving characteristics (and price) of a sports car has an energy consumption of 11 kwh/100 km with a range of 400 km on one battery charge (manufacturer’s data). The teslamotors uses lithium batteries, which have a particularly good charge-discharge efficiency.
The fuel consumption and CO2 figures given above for the citroen AX also apply in principle to many 5-door and 4-seater French electric cars (peugeot 106 electrique, renault clio electrique, citroen AX electrique), which can be operated as nearly 1-liter cars if their load and driving style are optimized.
One problem that remains unresolved is the barely feasible size of the battery for a driving distance of several 100 km. If batteries are installed that do not take up too much space and are not too heavy, one has to make very time-consuming recharging stops of several hours for this distance too often.
Low penetration of low-energy vehicles
Although series production of the three-liter car was welcomed in principle, it was discontinued again because demand did not justify the cost. The development of successor models to the VW lupo 3L TDI (z. B. On the platform of the VW fox) was set. Production of the audi A2 3L TDI was discontinued in mid-2005 without a successor. The smart cdi is gaining popularity precisely because of its low CO2 emissions – however, vehicle production has often been questioned and the original concept of the electric vehicle has not been offered in series production to date. The opel astra eco4 with modified bodywork has disappeared in the new model series.
The following are some points that often come up in the discussion about low-energy vehicles:
