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Zero and Low-emission Vehicles for cities.


This short report summarises the options available for addressing the problems of pollution caused by internal combustion (IC) engined vehicles in cities.

The IC engine can be highly efficient when running under optimum conditions at relatively constant speed - as in a car on a motorway - and such undesirable emissions as there are can be greatly reduced by catalytic converters. But the IC engine is relatively inefficient, with high emission levels of unburnt and partially burnt fuel, when running in city traffic - characterised by short journeys with cold starts, repeated stopping and starting, and long periods of tickover in traffic jams.

In previous papers (1), (2), we have shown that the US concept of the Neighbourhood Electric Vehicle (NEV) is potentially viable in suburbs, and that electric vehicles produce less emissions affecting the ozone layer than thermic vehicles, even when supplied from coal-fired power stations.

This paper examines the possibilities of reducing vehicle emissions in inner cities.


In Europe and the Americas most vehicle pollution comes from 4-stroke petrol engines in private cars and vans, and Diesel engines in taxis, buses and commercial vehicles.

In Asia there are less private cars, but there is a high proportion of 2-stroke engines in scooters, auto-rickshaws, tuk-tuks, tripoteurs &c, running on petrol-oil mixtures with levels of hydrocarbon emission s (from partially burnt fuel and oil) well in excess of levels permitted in the West. (2-stroke engines in vehicles such as trabant in former East European countries also fail to meet Western emission regulations and are being phased out as rpidly as is politically possible in view of the large number of owners). In Asia the level of pollution from diesel engines - already unacceptable in the West - is much higher because vehicles are expected to have a much longer life span and maintenance is less frequent than the manufacturers recommend.

These emission problems are often aggravated by hot and humid climates, to the extent that most major city authorities and governments in Asia are now actively seeking solutions to the ever-worsening environmental and health problems caused by increasing motor traffic.


An ideal solution would appear to be the burning of hydrogen in IC engines, as the combustion product is water. However, hydrogen is not easily produced or stored and its use is uneconomic at present. Second best are natural gas (mainly methane) and Liquid Petroleum Gas (eg propane), but much cleaner than liquid fuels in IC-engined vehicles; even cleaner is the small gas engine running at constant speed under optimum conditions used to drive an electric generator.

At the point of application battery-electric vehicles have zero emissions, but unless fuelled by renewable energy sources they will emit combustion products at the power station, but in a smaller quantity and in a more desirable and controllable location than the IC engine (2) - ie not in city centres.


We know from measurements taken on our own and other electric vehicles, that a typical 4-seat hatchback or small van of 0.85-1.0 Tons weight requires just over 3 Kilowatts (4-5 HP) to drive it at 30mph (50 kph). However it is generally fitted with an engine of 35 KW or more, partly to give it good acceleration (the IC engine has rather poor torque at low speeds so a more powerful engine is needed to give good acceleration, even with the change of ratio given by a gearbox) but also to provide a top
speed of up to 90 mph (at such speeds air resistance increases rapidly).


In spite of large expenditure on battery development around the world, the only vehicle batteries likely to be commercially viable over the next 5 years are existing lead-acid (LA) and advanced lead-acid (ALA) types. (For a given power Nickel Cadmium is 6-8 times more expensive than LA). LA gives about 2.5 KW Hrs of usable energy per 100Kg of weight. A 300Kg battery pack will
therefore be required to give a standard hatchback or small van a range of 50-60 miles at an average of 30mph, as discussed above.

ALA is claimed to give up to 50% more power for a given weight (eg the US Horizon battery) but at four times the cost of the much simpler and readily available LA. Thus, if 1/3 of the battery weight can be saved by weight-reduction in other parts of the vehicle - eg 100Kg saving with a 300Kg battery pack - the cheapest LA batteries offer a more viable solution. LA battery costs are about $225 (£150) per 100Kg or $90 (£60) per Kw Hr. (This compares with about $375 (£250) per Kw Hr for ALA and about $600 (£400) per KW Hr for NiCd).

To summarise then, the most viable zero-emission vehicles over the next 5 years will have conventional batteries and will be purpose-designed to save at least 100-300Kg in weight as compared with the equivalent IC-engined vehicle; they will have a range of 50-60 miles in city driving with a 300Kg LA battery pack, and possibly 100 miles with 500 Kg of batteries.

Lighter vehicles, such as auto-rickshaws and commercial 3-wheelers with a weight without batteries of 270Kg would probably achieve the above ranges with 180Kg and 300Kg of LA batteries respectively. Test results will be available shortly when London Innovation has completed conversion of the Bajaj auto-rickshaw due for delivery from India within the next 4 weeks.


Supposing a city of 10m inhabitants had electric vehicle ownership of 1%, each vehicle requiring 10- KWHrs of energy per day (allowing for charging inefficiencies &c).

If the re-charging period were 10Hrs, then the power flow on charging would be equal to: Total KwHrs divided by Charging Time = 10,000,000x0.01x10/10 = 100,000KW or 100MW.

As charging would be mainly carried out at night, this would have advantageous load-levelling implications for electricity supply. The exact effect would need to be determined in the light of local generating conditions - eg coal-fired generation would derive the biggest benefit.


The above section discusses the effects on electricity supply of the vehicle battery capacity only. If however, storage is introduced at eg re-charging stations, then there are further implications:

a. Flow of power from the electricity supply can be spread over 24Hrs, thus reducing installed power requirements further - eg to 42MW in the above case.

b. Current flow can be greatly increased to the vehicles, thus allowing rapid charging at currents of several hundred Amps per vehicle without increasing the power drawn from the electricity supply. This would be highly desirable for urban delivery and messenger vehicles.

c. Assuming a charging current of 300Amps - which is acceptable for Gates and similar batteries - this represents a power flow to the battery of 21.6KW.

Assuming a worst-case charging efficiency of 75% and a charging time of 10 hrs, total energy input will be 10 KWhrs at an average rate of 1KW. The battery pack could thus be increased up to 3 times - that is, up to 30 KWhrs, or a weight of 1200Kg - while the charger could still be operated from a 13Amp supply. Allowing for inefficiencies a battery pack of at least 1 ton could be charged from a 13Amp supply.


We have seen above that with present technology electric-only drives are viable for vehicles up to about one ton in weight and range up to 50-60 miles.

For vehicles over 1 ton and ranges over 50 miles some form of hybrid assistance is needed at the present state of battery development. As mentioned above, a small gas-powered generator running at constant speed can provide sufficient power for almost continuous operation in the stop-start conditions of city traffic.

This arrangement is ideal for taxis and larger vans. The generator pack can be sized to give the range required for any vehicle use. With the London taxi the capacity of the propane engine to drive the generator would be about 500cc, as compared to the 2.5 litre diesel engine normally fitted. The undesirable emissions from a small propane engine are likely to be less than 5% of those from the five-times-larger diesel engine.

Because the generator engine would be running at constant speed it could be tuned for maximum energy-efficiency, thus further reducing undesirable emissions and making it easy to silence. NOx would be inherently lower because of the lower combustion temperature. The marginally higher efficiency of the Diesel engine would be offset by the smaller size and constant-speed running of the propane engine.

Maintenance costs would be much lower as the propane engine is smaller, it would be mounted in a removable sound-proofing capsule which could easily be taken out of the vehicle and serviced on the workshop bench, thus avoiding the need for hoists and working under the vehicle.

Natural gas is marginally cleaner than propane having a higher hydrogen content; but not being easily liquefied, it must be stored in heavy, high-pressure cylinders and is not readily available. On the other hand, propane is sold at many service stations, caravan suppliers and builders' merchants.


Huge investment has been made in present forms of transport, and improvements are likely to come about only through strong government action under pressure from public opinion, which is becoming increasingly aware of the environmental and health hazards from the heavily polluted atmosphere in most of the world's cities.

"Strategic Legislation" - eg California's requirement that 5% of vehicles sold from 1998 must be zero-emissions-is probably the strongest spur to the development of improved technology. Governments should declare that designated city centres should have zero emissions by the year 2000. In London Westminster council should legislate that Oxford St and its environs become a `clean air island' by the year 2000. This would make a big impact in the campaign to clean up the London taxi as it is well known that Oxford St is one of the most polluted areas in the country, yet it is closed to cars and therefore the present pollution can only come from the Diesel engines of buses and taxis.

London Innovation's* involvement could be to

a. Develop cheap and efficient hybrid vehicles, using the Lynch motor and simple but appropriate technology to go with it - batteries, controllers, chargers &c. - to comply with whatever regulations governments decide to impose.

b. Produce the first prototype and demonstration vehicles of any type - eg urban van, scooter, auto - rickshaw, triporteur &c - to prove that the concept is viable and that the hardware could be produced if required to meet more stringent regulations.

* London Innovation is the innovation centre which has backed the Lynch motor's development since 1985.

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