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October 1st, 2005:

Cleaning Up The Bus Fleet

Cleaning up the fleet

October 2005

by Fung Man Keung

Lecturer, Department of Automotive Engineering,
Hong Kong Institute of Vocational Education

When concentrating on emission quality only, particulates and nitrogen oxides are the main foci as revealed in Euro IV and V standards.

There is no doubt that liquefied petroleum gas (LPG) is superior to diesel because of its homogenous combustion characteristic, where only very tiny particles and pollutants are emitted. A diesel fuelled engine, with its inherent heterogeneous combustion process, promotes higher concentration in the said pollutants. That’s what we care about.

In Hong Kong, the EPD says that the concentration of diesel engined vehicles is too high. We could add to this and say that the concentration of purely mechanical and unsophisticated / older diesel engined vehicles is too high.

However, applying the state-of-art technology in engine design and after-treatment devices enables them to comply with stringent emission Regulations; therefore, the ban on new light diesel vehicles may not be persuadable enough especially when they comply with latest emission requirements;

You may find that almost half of the new light vehicles in Europe are diesel fuelled and many well known manufacturers are putting a lot of effort into light diesel vehicle research and development and hence manufacturing much cleaner engines.

Diesel possesses a higher energy density compared with various other types of fossil fuels which are commonly used in vehicles. About 40% higher than liquefied petroleum gas (LPG), and diesel engines achieve a higher thermal efficiency compared with spark ignition (LPG or gasoline) engines which may be the driving force for the manufacturers to develop diesel vehicles more aggressively.

From an energy conservation point of view, diesel is therefore the best choice to reduce energy consumption because global warming gases are reduced as a consequence.

In our opinion, new diesel vehicles which comply with the latest emission regulations should have the right to play the fair game with other types of engines;

But… we should make every effort to ensure the emission quality during their service life remains high instead of simply banning them. More frequent monitoring, say biannually, and up-to-date standards for used / older vehicles will be an effective measure to maintain a lower pollution level.

Whichever the type of vehicle, engine deterioration is the prime factor in the decline of emission quality, especially high mileage, public service and commercial vehicles;

Unfortunately, engine deterioration caused by vehicle age and mileage is not part of the existing inspection criteria. Instead, a highly tolerable (easy to meet) emission standard is applied to all vehicles whether they are just 2 or over 10 years old, for instance.

How can owners be encouraged to upkeep their new or lower age vehicle close to the original emission quality? Right now, most vehicles on road just comply with the emission standards of ten years ago or even earlier.

Emission standards for new vehicles are reviewed from time to time in order to aim towards the goal of zero emission; in the meanwhile, if the standards for those vehicles on road are not revised according to their manufacturing year, the road to improving air quality in Hong Kong will be greatly prolonged.

In summary, we would need to realize that all combustion engines are harmful to the environment. Due to the ever developing technologies the differences between the emissions from internal combustion engines burning differing kinds of fuels are diminishing.

We can no longer single out one engine as being very much worse than another (e.g. dirty diesels).

Arguably the key factors to ensuring that engines run as cleanly as possible are

  1. application of the latest technologies
  2. effective maintenance
  3. use of high quality / clean fuels, and
  4. high durability of any given product or system

No matter how clean the emissions of any given internal combustion engines are, such engines will still emit large amounts of carbon dioxide and raw heat, but the toxic gases / particles will likely be greatly minimized.

Any given jurisdiction should take steps to carry out regular emissions checks on all vehicles, say once or twice per year. The data should be collected and analyzed to see where the problem areas are and then corrective actions explored / taken.

Polluting vehicles should be rejected from being reregistered on the road to ensure that good maintenance is applied across the whole Hong Kong fleet.

It therefore follows that having the most stringent regulations is quite useless unless these are matched with appropriately stringent enforcement.