select search filters
briefings
roundups & rapid reactions
Fiona fox's blog
This was in light of ongoing investigations into whether contaminated petrol was behind a problem which affected the engines of hundreds of cars across Britain.
Dr Clifford Jones, Reader in the Department of Engineering at the University of Aberdeen, said:
“Some crude oils naturally contain silicon so finding silicon in petrol is not necessarily cause for alarm as silicon occurring naturally would not be in sufficient quantity to cause the difficulties reported by the motorists this week. However, larger amounts of silicon if introduced into the fuel in some way could damage oxygen sensors and this is one possible explanation.
“There have been suggestions that the oxygen sensor, which ‘informs’ a car’s engine management system, has become blocked in the affected cars. It is counterintuitive but not impossible that petrol causing an ‘unclean burn’ has caused this through particle deposition. In any case oxygen sensors in normal use do become blocked with time and need replacing.”
Andrew Furlong, Director of Policy & Communication, Institution of Chemical Engineers, said:
“The problems appear to be affecting drivers who have purchased fuel that has been blended with up to 5% of bioethanol. This is a legitimate practice and one that is being driven by European environmental legislation.
“Bioethanol is renewable and can help cut CO2 emissions. The addition of bioethanol can also help reduce the amount of harmful benzene type compounds that have been used to improve the quality of petrol sold on garage forecourts.
“Bioethanol increases the amount of oxygen in petrol. The maximum allowable oxygen content is 2.7% and stringent testing is carried out by oil refiners and companies involved in blending petroleum products.
“Press reports suggest that drivers are experiencing difficulties with the engine management systems that are a feature on modern cars. Whilst fuel with excessive oxygen content may cause performance problems and even stalling, permanent damage is unusual.
“Nonetheless, chemical engineers have urged caution in the uptake of biofuels. The modern car engine is a highly developed and finely balanced machine as drivers in the South East have discovered to their cost. What we are seeing here may just be the downside of the popular rush to embrace biofuels.”
Brian Robinson, Head of Environment, Institution of Mechanical Engineers, said:
“Ethanol mixed with petrol should cause no problems in cars designed to run on conventional unleaded petrol at blends of around 10% or less (i.e 10% or less of ethanol, 90% or more unleaded petrol).
“The problem is, we don’t know the extent of this problem – and consumers filling up won’t know if the fuel they are putting into their cars has the right/wrong amount of ethanol – if that is the irritant.
“Let’s say, for the sake of argument, that the fuel contained significantly more than 10% ethanol, then the problems would include damaged fuel system, rubber seals, and damaged engine parts, especially those made of aluminum, from the extra acidity of the high ethanol blend fuel.”
Prof Paul Shayler, Professor of Mechanical Engineering, University of Nottingham, said:
“The problem appears to be on petrol engines only. No problem with diesels: these run on a different fuel and don’t use oxygen sensors.
“Oxygen sensors are located in the exhaust gas stream towards the upper end of the exhaust system. These days there may be more than one, in front of and after the exhaust catalytic converter. They detect the partial pressure of oxygen in the exhaust gases. Their prime uses are to provide feedback information to the engine management system on a) the ratio of fuel to air being supplied to the engine cylinders and b) to check that the exhaust catalytic converter is operating correctly. The simplest feedback tells the engine management system if the ratio of fuel to air being supplied to the engine cylinders is rich or lean of the correct (stoichiometric) value required for the exhaust catalytic converter to work efficiently. The engine management system uses this information to reduce or increase the ratio so that it cycles back and forth across the stoichiometric value, although it is such a small deviation that the driver should not be aware this is happening.
“If the oxygen sensor(s) fail, the engine management system will usually detect something is wrong and enter a ‘limp home’ mode and flag up a warning to the driver. In this default mode, the management system is usually able to make a good estimate of what the ratio of fuel, and this should avoid the heavy misfiring which is being reported, so it may be the failure of sensors is perhaps another symptom of whatever is causing misfiring and lack of power.
What could it be? The sensors can fail through poisoning or the build up of deposits. I haven’t seen anything on the news which looks like a sensor with obviously ‘sticky’ deposits. The misfiring suggests spark plug deposits – again easy to spot so unlikely. More likely, the engine is being supplied with very lean mixtures. If the engine is operating in default mode, it might be the fuel injectors are not providing the fuel quantity the engine believes they are and is no longer able to check. It might be that the contamination is clogging or affecting the lubricating properties of the fuel.”
Mr Brian Baker, Association For Petroleum And Explosives Administration , said:
“This level of wide spread fuel contamination is extremely rare. The more common cause of fuel problems is misfueling an example of which might be putting diesel in an unleaded car. This is often due to confusion at the pump as the refuelling becomes increasingly complicated with names, colours indicators and range varying with each retailer.
“All aspects of the fuel supply in this country are regulated by the BSEN 228 standard which describes what fuel can contain. At this stage there is no clear source of the contamination but there are a few possibilities. The large chain fuel outlets like the supermarket chains have significant purchasing power which means they can by fuel at the best price from a variety of suppliers. This includes imported fuel which may be one source of concern in this case.
“We also need to establish which fuel distribution depot this fuel has come from. Fuel distribution depots are dotted around the country, for London and the south east the Coryton depot is Essex is one of the main suppliers. All fuel is checked for quality before it is loaded onto the tanker at these depots although a failure to pick up contamination at the distribution level could explain the wide spread problems which seem to be occurring. If this was simply a case of the wrong fuel being but in the wrong container at the service station level you would expect a highly localised problem. This however appears to be a national problem which points higher up the distribution chain than an individual petrol station.
“An in depth analysis of fuel samples is a complex process which very few places in the UK are qualified to carry out. This means that it will take some time to identify the source of contamination. But this analysis should indicate whether it is a national problem or if it is confined to one supplier.”