Exhaust Emissions

Transport written question – answered on 12th February 2004.

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Photo of Bob Spink Bob Spink Conservative, Castle Point

To ask the Secretary of State for Transport what the comparative motor vehicle exhaust emission statistics are for (a) liquefied petroleum gas, (b) compressed natural gas, (c) petrol and (d) diesel.

Photo of Mr David Jamieson Mr David Jamieson Parliamentary Under-Secretary, Department for Transport

The comparative statistics in the tables are taken from the joint DfT/HMT consultation 'Road fuel gases and their contribution to clean low-carbon transport' released in June 2003.

The figures allow a comparison of the mandatory European emission standards for new petrol and diesel vehicles in comparison with typical emissions from LPG and Natural Gas vehicles.

Several sources of uncertainty arise when assessing the performance of LPG vehicles. The level of emissions improvement in LPG cars depends heavily on the particular engines and conversions involved and on the standard of conversion. For these reasons, absolute comparison of LPG and conventional cars is not possible. The table gives an indication of the comparative figures.

Emission limit levels for new passenger cars—Conventional fuel cars and LPG cars
Diesel (g/km) Petrol (g/km)(10)
Conventional fuel cars—EU emission limits
Euro III—mandatory from 2001 0.50 0.05 0.15
Euro IV—mandatory from 2006 0.25 0.025 0.08
LPG cars—indicative performance(11) LPG NOx (g/km)
2002–03—typical powershift approved aftermarket conversion n/a n/a 0.123
2002–03—typical OEM ('Original Equipment Manufacturer') LPG car n/a n/a 0.035

(10) No PM limits for petrol or LPG vehicles, since emissions are very low.

(11) Data provided by Energy Saving Trust

Compressed natural gas is primarily used as an alternative fuel for heavy goods vehicles. The following table was included in the road fuel gas consultation document and shows the comparative performance of a natural gas version of one widely used vehicle, compared to EU diesel standards.

Natural gas emissions—performance of a Scania re-engineered vehicle, compared to EU limit values heavy duty vehicles g/kwh(12)
Emission limits Test cycle NOx PM10
Diesel vehicle
Euro III (13)ETC 5 (14)0.16 and 0.21
Euro IV ETC 3.5 0.03
Euro V ETC 2.0 0.03
Natural gas vehicle
CNG Scania vehicle(15) ETC 0.96 0.007


(12) http://europa.eu.int/comm/enterprise/automotive/pagesback/ pollutant emission/pollutant.pdf

(13) European Transient Cycle

(14) For engines having a swept volume of less than 0.75 dm3 per cylinder and a rated power speed of more than 3,000 min-1

(15) CNG Emission Tests based on Scania re-engineering programme Millbrook Vehicle Emissions Laboratory g/kwh

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