Gasoline direct-injection (GDI)

As spark-ignition internal combustion engines are immensely wasteful, vehicle manufacturers have strived to improve them for decades. Prompted by legislation, manufacturers introduced GDI – some would say too quickly – to enhance fuel efficiency and reduce CO2 outputs.

A more recent trend has seen GDI engines being downsized, which reduces cylinder capacity but introduces other technologies (including turbocharging) to produce very high outputs for a comparatively small engine size. While Europe became an early adopter, other countries are following: the US Department of Energy states that GDI was America’s most popular fuel-reducing technology in 2018.

While this has left back-slapping politicians and car company executives trumpeting their supposed environmental achievements, the real-world situation is not so rosy. Depending on which figures you believe, GDI engines produce between 1000 and 2000 times more carcinogenic particulates than older port-injection designs. This has been known for some time – the now defunct Euro VI emissions legislation, for example, had the same particulate limits for petrol and diesels. Only now is the situation starting to be redressed, with particulate filters being introduced on a very limited range of GDI engines. The situation also makes a mockery of certain direct-injection hybrid cars, which are exempt from MOT emissions testing – little wonder that our real-world air quality is so poor in major cities and apportioning all the blame onto diesel alone is not a satisfactory answer. Despite this, DIY mechanics and used car buyers are more interested in reliability reducing significantly as the car ages.