Although acclaimed for their near diesel economy, high levels of particulates emissions could outweigh the other advantages of lower hydrocarbons (HC) and fewer nitrous oxides (NOx).
Some industry experts believe DIs will require an expensive fix before the introduction of Euro V emissions regulations in three to four years’ time.
Despite claims of cleanliness, the DIs might need to be fitted with particulates filters similar to those used on diesels. It’s a move that may prove too costly for some carmakers.
Cash-strapped Mitsubishi has already steered away from the GDI (gasoline direct injection) system, but Volkswagen Group remains heavily committed to its ultra lean burn FSI engines.
Honda uses a DSI unit in Japan, but says there are no plans to launch it in Europe – its immediately forthcoming petrol engines will feature variable valve technology with conventional injection. Ford and Vauxhall have also gone quiet on their GDI developments: neither Ford’s Duratec 1.8 SCI nor Vauxhall’s Ecotec 1.6 and 2.2 are widely applied.
Toyota, however, claims its D-CAT Avensis will already meet Euro V when the European Commission eventually works out the new emissions standards.
But the latest generation Castrol Clean Performance Technology lubricants, specified as part of extended drain and Euro V targets for diesel engines by the likes of BMW, Volkswagen, Audi, Mercedes-Benz, Ford and General Motors, could offer a partial direct injection lifeline.
The lubricants maker says tests prove its new oils can help reduce particulates emissions from both diesel and DI petrol engines. Castrol insists that direct injection petrol engines produce more particulate matter than Euro IV capable diesels fitted with diesel particulate filters (DPF).
“We believe there is a clearly understood case that gasoline engines in general, and GDI engines in particular, do produce more particulates than latest specification diesel engines,” says John Moffa.
“We are not at the moment specifically claiming our Clean Performance Technology benefits GDI engine particulate output, but it would be quite surprising if it didn’t. We may wish to look at this more closely.”
Moffa agrees that stratified charged direct injection can give petrol engines an efficiency resembling that of modern diesels. But he adds that DI also makes petrol units inherit two main defects from diesel. The first is nitrous oxide after treatment in an oxygenated environment, meaning an NOx trap is already required and is, in fact, fitted to current GDIs. The second is increased particulates generation. “Particulates filters for DIs could become necessary, depending on future regulations,” says Moffa.
VW’s FSI technology – how it works
The introduction of the 1.4-litre, 87bhp FSI engine to the Polo early in 2003 marked the first use of new direct-injection petrol technology by Volkswagen in the UK market. It has since been followed by 1.6-litre, 2.0-litre and 3.2-litre FSI engines in an increasingly large number of VW, Audi, Seat and Skoda models.
FSI uses stratified direct injection in a similar manner to that employed in TDI diesels. The fuel is injected into the combustion chamber at high pressure and reduced consumption is achieved in low and medium speed ranges.
Direct petrol injection is used to control precisely the quantity of fuel injected and the fuel spray pattern. This brings the petrol engine closer to the efficiency of the diesel – compared with other petrol engines of equivalent power, it can provide an improvement of around 15% to fuel consumption.
Another benefit of this new engine technology is the efficient exhaust treatment of oxides of nitrogen (NOx) through a special catalytic converter. The result is improved performance and efficiency.
VW says FSI technology delivers immediate benefits on standard quality petrol but, due to the way in which it works to reduce NOx emissions, it provides further reductions in fuel consumption when sulphur-free petrol (containing a maximum of 10ppm of sulphur) is used.