Tighter in-service emission limits: let's get real

By: Alan Bunting, Thursday, September 10, 2009,

AutomotiveWorld.com

Following one of its recent plenary sessions, the European Economic and Social Committee (EESC) declared that "emissions from private, public and goods road transport continue to cause serious illness and erode quality of life, especially for urban populations, representing more than 75% of European citizens".

The EESC went on to criticise current EU emissions legislation. It highlighted the difference in permitted pollutant levels - of NOx (oxides of nitrogen), PM (particulate matter), HC (gaseous hydrocarbons) and CO (carbon monoxide) - between vehicle/engine certification values and those applied once vehicles have gone into service.

On-board diagnostic (OBD) systems, when used to monitor in-service exhaust emissions, allow levels up to 100% higher than the statutory limit - to which new vehicles must conform - before the driver receives an audible or visual warning. By the same token, the limits applied during roadside spot-checks and routine testing station procedures are significantly above those laid-down in either steady-state or transient cycle new-vehicle certifications.

In its declaration, the EESC accordingly recommended that "European Community Institutions take immediate steps to strengthen control measures, thereby protecting citizens' health". But, as is so often the case, those who sit on committees such as the EESC, though they might have the most honourable intentions, are too far removed from the practicalities on the ground.

They need to realise that the accuracy of emission measurements achieved in certification testing, under laboratory conditions, reliant on a costly computer-controlled dynamometer to regulate engine load, cannot be reproduced using relatively modest OBD or portable exhaust sensing equipment.

Great strides have been made, by suppliers such as NGK in Japan, in the accuracy and repeatability of compact and portable sensor readings, for NOx in particular. That has enabled the threshold above certification limits, allowed for in-use emissions measurement, to be progressively reduced.

But the likelihood of headline certified emission limits ever being applied directly for in-service conformity is remote. It must be recognised too that those limit thresholds, which effectively constitute a necessary margin for error, also provide a margin for some deterioration (ie wear and tear) through the life of the engine, even though the latest Euro 6 legislation includes what amount to minimum conformity lifetimes - expresed in kilometres for different commercial vehicle weight categories.

The opinions expressed here are those of the author and do not necessarily reflect the positions of Automotive World Ltd.

Published on Thursday, September 10, 2009