Citroën C3 1.6 e-HDi

What is it?

A Citroen C3 powered by Peugeot-Citroen’s EU emissions legislation trump card: a micro-hybrid diesel powertrain called e-HDi.

By 2012, PSA is aiming to sell a million cars in Europe every year that emit less than 120g/km of CO2, and most of them will be powered by this engine.

Diesel-sipping ‘stop-starts’ are much less common than petrols because, since diesel engines have higher compression ratios, heavier crankshafts, flywheels and balancer shafts and greater internal friction, they take more re-starting. Those diesel micro-hybrids that do exist use beefed-up starter motors and gearing systems that, claims PSA, are unsuited to fast, smooth hot starts.

So the French automaker has developed a stop-start system driven not by the car’s starter motor but off its alternator. Backed up by two ultracapacitors as well as a conventional battery, the alternator motor can supply 50 per cent more torque to the crankshaft than a conventional ‘ISG’.

That means its gearing can be higher and its engine restart performance faster. And because the stop-start system has a separate belt drive, it restarts the engine more quietly and smoothly than others too.

What’s it like?

The e-HDi system will appear on PSA diesels ranging from 1.4- up to 2.0-litres. In a 1.6-litre Citroen C3, it’s smoothness and speed of operation was very impressive indeed.

Here’s how it works. In a manual, the car must be in neutral and your foot off the clutch before the system will cut in. You don’t have to be stationary: below 13mph it’ll kill the engine if it thinks you don’t need it, but can restart it within 400 miliseconds.

Faster than you can dip the clutch and re-engage a gear, in other words.

Should I buy one?

Perhaps not if you’re looking to make an environmental statement. Despite its low rolling resistance tyres, taller gear ratios, low viscosity gearbox oils and intelligent ancilliaries, e-HDi is only worth five grams per kilometre on a car like the C3.

On a Citroen C5 or Peugeot 508, it’ll save more like 10g/km of CO2 – but that’s still not a great deal. It also encourages you to coast along out of gear in town, which we wouldn’t recommend as a driving technique.

As a cheap and unobtrusive way to make PSA cars a little more efficient, however, we approve of e-HDi. On a typical new Peugeot or Citroen, the system should cost you a few hundred pounds as of later this year, save you 15 per cent on urban fuel consumption, and deliver savings on VED road tax too.

If it proves reliable, it would be among the first options we’d choose.

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