My internship project involves looking at the best way of introducing 2 and 3 wheeler electric vehicles (EVs) in developing countries.
However, at the outset I felt I needed to do more work on why EVs were being pushed over, say CNG vehicles, more efficient IC engine vehicles. The following post thus looks at different types of vehicles and their relative pros and cons.
1) Diesel versus Petrol vehicles. Note that countries like India have subsidized the cost of diesel, leading to a forced substitution of petrol vehicles with diesel vehicles (there is a Rs 30 difference between the two). In the US, however, petrol and diesel cost roughly the same. In 2007, petrol costed $3/gallon, while diesel cost $3.39/gallon.
Is this shift from petrol to diesel good? The following table compares petrol and diesel.
The carbon dioxide emissions for petrol are higher. It emits 13% more CO2/gallon of fuel burnt. However, note that diesel is 1.5x more efficient than petrol. This is because diesel engines can operate at higher compression ratios than petrol, and there is no risk of auto-ignition.
In the past, diesel engines were considered noisy (the sound emitted in the exhaust blow down in diesel engines is louder than petrol engines as they operate at higher pressures) and dirty, and therefore they were not used, in spite of the fact that diesel is more efficient than petrol. In order to produce cleaner, quieter diesel cars, they were fitted with a trap to catch particles of smoke in the exhaust. However, these traps in many places, were seen to not work properly unless the vehicle was hot, and many drivers removed them.
Diesel produces more NOx than petrol engines, and more particulates. Catalytic converters could be used to lower NOx concentrations. Unfortunately, many diesel fuels contain S at concentrations that could foul the converters.
New diesel engines have an electronic ignition system that compensates for cold starts and has self cleaning features.
Petrol engines produce more CO (when they are being warmed up)
Petrol engines emit more hydrocarbons (HCs)- containing harmful substances such as benzene
Diesel engines are heavier than gasoline engines of the same power because diesel requires a larger cylinder displacement for complete combustion, and heavier components to withstand higher pressures and temperatures.
For small vehicles, the weight penalty diminished the advantage in fuel from 40% to 20%
Gasoline engines after the 1980s can use mixtures of gasoline and up to 10% ethanol without modification. With modification (fabricating the engine from materials that are resistant to ethanol/methanol corrosion and installing sensors that detect the fuel mixture and allow the electronic ignition control unit to adjust the engine timing)- this can increase.
Converting a gasoline engine to use CNG involves the addition of a pressure regulator and an electronic multi-point gas injection system similar to a gasoline injection system.
Diesel engines are more flexible in their fuel mixtures. Rudolph Diesel ran his vehicle on vegetable oil.
2) 2 stroke versus 4 stroke engines
2 stroke engines are lower cost. They are lighter and are smaller, thanks to their mechanical simplicity. Due to this simplicity, they have greater operating smoothness. However, as compared to 4 stroke engines they are noisier, have lower fuel economies, emit more particulates and HC emissions. This is due to the fact that 15-40% of the unburnt fuel-air mixture escapes through the exhaust valve. Oil is used as a lubricant and is usually mechanically introduced continuously to the fuel/air mixture. The incompletely combusted lubricant and other heavy HCs are emitted as oil droplets and result in increased smoke and increased PM. 2 stroke engines have lower NOx emissions.
Due to the tightening of emission standards there has been a shift from 2 stroke engines to 4 stroke engines. However, the exact effects of running these 2 engines has not been characterized perfectly and there is still work to be done.
2 stroke gasoline engines and heavy duty diesel vehicles are major contributors of PM10.
However, it is noted that the age of the vehicle is an important determining factor due to rapid improvements in engine technology recently. In the US it was found that 20% of the vehicle fleet was responsible for 80% of all emissions.
3) Biofuels
Biofuels may be in the form of ethanol or biodiesel. While ethanol is made from fermented sugars, biodiesel is made from the oil of certain plants.
Although corn-based ethanol is now the dominant biofuel in the US, criticism over this type of ethanol is increasing. Cellulosic ethanol now promises to play a leading role in the future of biofuels. Ethanol is mainly used as a blending agent with gasoline to increase the octane number and decrease CO and other smog-causing pollution.
Biodiesel can be used as an additive (typically 20%) to reduce vehicle emissions or in its pure form as a renewable alternative for diesel engines. Organizations such as NREL are researching the production of liquid transport fuels using microalgae
Biofuels can be 1st or 2nd generation fuels.
1st generation biofuels are made from sugar, starch, vegetable oil. They differ from 2nd generation biofuels, in that their feedstock is not sustainable or, if used in large quantities, would have a large negative impact on food supply. 1st generation biofuels are the 'original' biofuels and constitute the majority of biofuels currently in use.
2nd generation biofuels are 'greener' in that they are made from sustainable feedstock.
George Monbiot argues in several Guardian pieces in 2012, that biofuels are means by which governments in the rich world avoid hard choices. Rather than raising fuel economy standards, promoting non motorized transport etc, they have chosen to invest heavily in biofuels.
The US and EU set targets and created generous financial incentives for biofuels. In 2012, 40% of US maize production was used to feed cars. Although the market for biodiesel is largely confined to the EU, it has already captured 7% of the world's vegetable oil output. The EU commission has admitted that its target (10% of transport fuels by 2020) would raise world cereal prices by between 3% and 6%. Oxfam estimates with every 1% rise in the price of food, 16 million people go hungry.
By 2021, OECD says that 14% of the world's maize and other coarse grains, 16% of its vegetable oil and 34% of its sugar cane will be used to produce biofuels.
ActionAid has also estimated that European countries have seized 5 m hectares of farmland (an area the size of Denmark) in developing countries for industrial biofuel production.
When the impacts of land clearance, and the use of nitrogen fertilizers are taken into account, biofuels produce more GHG than fossil fuels. 'Burning biomass instead of fossil fuels does not reduce the C emitted by power plants' a group of 78 scientists wrote to the EPA Director against the new power plant policy. 'Burning biomass, such as tree, that would otherwise continue to absorb and store C comes at the expense of reduced C storage.'
However, last year the IPCC stated that riddled with the usual uncertainties of science, being < 2 degrees C would be much harder without biofuels?! Absent a big increase in bioenergy supplies, the climate change panel's analysis reported, it would cost about 2/3rd more, on average, to prevent the earth's temperature from rising more than 2 degrees C. In most models that bring temperatures back under the 2 degrees C ceiling by the end of the century, biofuels are assumed to produce about 250 to 350 exajoules of energy/year. 300 Exajoules is > than half the world's current energy consumption. Today, the energy content of all the biomass harvested for food, fodder and everything else amounts to about 220 Exajoules.
Where will the land to produce these biofuels come from? If the productivity of agriculture and livestock were the same all the world over, as in developed countries, the world could feed 35 million people. In that case, deploying just 10% of the world's 5 billion hectares currently used for crops/pastures could generate 100 to 150 exajoules by the end of the century.
However, other environmentalists such as George Monbiot question the practicality of such calculations.
He states that even second generation biofuels made from crop wastes or wood are an environmental disaster, either extending the cultivated area or removing the straw and stovers which protect the soil from erosion and keep the C and nutrients in the ground.
4) Synthetic fuels: Substituting diesel and jet fuel can be produced from different feedstock converting biomass to liquid (BTL), coal to liquid (CTL) or gas to liquid (GTL). Hydrotreated vegetable oils (HVO) of a similar paraffinic nature, can be produced by hydrotreating plant oils and animal fats. Synthetic fuels can be distributed, stored and used with existing infrastructure and existing internal combustion engines. They offer a cost-competitive option to replace oil-based fuels with the perspective of further imporved system performance with engines specifically adapted to synthetic fuels. The EU has the development of industrial scale plants for the production of cost-competitive synthetic fuels derived from biomass as a high priority.
EU policy reports state that efforts should be continued to improve the CO2 balance of GTL and particularly CTL. DME is another synthetic fuel produced from fossil or biomass resources via gasification (synthetic gas), requiring moderate engine modifications.
5) EVs versus CNGs
EVs are more efficient than CNG vehicles.
1000 cubic feet of CH4 provides 457 miles in an EV, and only 224 miles in an NGV
NGV have lower efficiencies than hydrogen, hybrid, gasoline, diesel and electric vehicles.
The filling time of an EV (240 V charger) is 3-8 hours. Building an electric charging station costs $2000 (including installation costs). DC fast chargers cost around $50,000. CNG filling stations costs $750,000, however, the filling time is a few minutes.
The vehicle cost is a tossup.
If one looks at fuel costs, EVs win according to Forbes Magazine
In terms of range, a 4 door CNG taxi with a trunk can hold the equivalent of 15 gallons of fuel and can get close to 300 miles on a tank. EVs get about a 100 miles.
6) LPG is a by product of the hydrocarbon fuel chain. It is currently the most widely used alternative fuel in Europe accounting for 3% of the fuel for cars and powering 5 million vehicles. More than 27,000 filling statons currently exist in Europe
7) Electric Vehicles (EVs)
Electric cars dominated the automobile car market in the second half of the 19th century. However, the low energy density of batteries at that time lost out to the high density, cheap, plentifully available fossil fuel. However breakthroughs in battery technology today has led to a resurgence of talk around EVs.
Electric propulsion of road vehicles occurs in the following configurations
1) Hybrid Electric Vehicles (HEV): These use a combination of an ICE engine and an electric motor. The battery is charged from braking energy recuperation. The external energy input comes only through the fuel of the IC engine.
2) Plug-in HEV: It uses the same power train as an HEV, but with the additional option of charging the battery also by plugging to the electricity grid.
3) Range-extender Vehicle (REV): It represents another type of HEV with propulsion from an electric motor, and charging of the battery by plug in to the electricity grid or by a petrol fueled ICE. When the battery is depleted, a small ICE working as a generator provides the electricity for propulsion and for sustaining the battery state of charge
4) Hydrogen/Fuel Cell Vehicle (HFCV), with electric propulsion only, and external energy input through refilling an on-board hydrogen tank
5) On-board reformer, where the car is fueled with either bioethanol or biomethanol and the reformer converts the biofuel to hydrogen. This may provide extended operational range
6) Trolleybuses with overhead wires
Hydrogen fuel cell vehicles are similar to BEVs in terms of having a high efficiency power train. A key difference between both technologies is the upstream GHG emissions associated with the generation and delivery of the energy carrier. Two key aspects that affect the visibility of HFCVs are related with the hydrogen storage and production. Producing hydrogen by hydrolysis is an energy intensive process and requires 3x more energy, and thus emits 3x more GHG than a BEV. However, studies say that the use of HFCVs in a scenario where electricity is obtained from RESs could have advantages over BEVs to achieve a higher autonomy.
Electric motors replacing conventional ICEs can improve the efficiency of light-duty road transport vehicles by a factor of 3. The improvement for heavy-duty vehicles is closer to a factor of 2, compared to a diesel ICE drive train.
However, the energy density of vehicle batteries is much lower than that of gasoline/diesel (even Li ion batteries are an order of 50 lower in energy density). Therefore, even with a factor increase of 5x in efficiency, would still require a 15x larger weight.
Adding a small ICE or fuel cell to the electric drivetrain though, has the potential to overcome the range limitation of pure EVs.
Studies which have looked at the comparative environmental life cycle assessment of conventional and electric vehicles, however, indicate that such a comparison depends heavily on the electricity mix being used by a country. EVs powered by the European mix, offer a 10% to 24% decrease in Global Warming Potential (GWP) relative to conventional diesel or gasoline vehicles assuming a lifetime of 150,000 km (note a vehicle lifetime of 200,000 km, the GWP benefits of EV is 27-29%). However, EVs exhibit the potential for significant increases in human toxicity, freshwater ecotoxicity, freshwater eutrophication, and metal depletion impacts largely emanating from the vehicle supply chain
Another study looked at the lifecycle GHG emissions of EVs for different energy mixes. It was found that this number was 979gCO2 equivalent/kWh for a fossil fuel mix, and 100-300g CO2e/kWh for a mix with more renewables.
Note that this post provides a taster of the difficulty in choosing between different types of cars. Also note that CO2 emissions are not the only environmental axis to make such valuations. Other emissions such as particulates, NOx are equally important considerations


