IN PRAISE OF DIESEL

The word “diesel” has only to be mentioned for luddites such as Mike Dunstan (Letters, last week) to start talking about “particulates, particulates”.

All internal combustion engines emit particulates; diesels emit some PM10s (particulates of 10 micrometers or less) but petrol engines emit even smaller (and possibly more harmful) PM5s.

Petrol engines also emit benzene, which is a proven carcinogen, unlike PM10s, and have to be fitted with catalytic converters to reduce emissions of carbon monoxide by converting it to CO2. Petrol is also toxic, explosive and generally not nice stuff at all.

Diesel is much safer and more benign. If it’s biodiesel it’s even largely biodegradable and if it’s straight vegetable oil you can eat it. Mile for mile, diesels produce fewer emissions than petrols overall.

Stephen Eeley, St Ives, Cambridgeshire

FULL OF ENERGY

Peter Martin (Letters, March 30) wonders why diesel fuel is more expensive than petrol. There has been a move in recent years to price and tax fuels according to their energy content. Diesel has a higher density than petrol, in the ratio of approximately 1.1 to 1. Thus there is about 10% more energy in a litre of diesel than in a litre of petrol. The price reflects this. The reason diesel was originally cheaper was that it was believed it produced cleaner emissions. That has since been discredited.

Gerald Billington, Spital, Wirral

FAIR-WEATHER HIKERS

I have hiked and camped in both Britain and the United States and found Will Robson’s article “Head for the hills – with as little as possible” (InGear, last week) excellent in promoting a lightweight approach to hiking and camping. I agree with much of what he writes, with two exceptions.

First, the “safety brigade” have fortunately not had a big impact on hiking in the UK. The safety advice and support offered by official bodies, such as the British Mountaineering Council, is in proportion to the risks involved in hiking in the mountains.

Second, the ultralight hiking movement originated in the US, where for many long-distance hiking trails the weather is more predictable and less variable than in the UK. I have hiked and camped in the Loch Hourn region of northwest Scotland, and trainers, a poncho and the shelter of a nylon sheet are not appropriate for this wet and windy region. Boots, lightweight full waterproofs and a tent are required to hike in comfort and safety.

John Robinson, Aberdeen

DIY ADVENTURE

Lightweight travel isn’t a new phenomenon. When you get past the Boy Scout/Duke of Edinburgh award stage it doesn’t take much to work out that pleasure is inversely proportional to the weight in your rucksack.

There have been notable examples in the past – Tilman cycling through Africa; Alexandra David-Néel wandering through the snows of Tibet (not even a rucksack; everything concealed under her clothing); not to mention all those travellers who learnt from the natives how to live off the land.

Robson has missed a few tricks: that waterproof poncho will double up as a shelter (no need for the tarpaulin); or you could use an old shower curtain, which is just as effective. Couscous is the ideal carbohydrate; pour into boiling water and leave for a few minutes.

Can we have some more articles about DIY adventure? There are plenty of us doing it.

Vic Brown, Felton, Northumberland

FORMULA FUEL

In his letter last week Richard Caddy asks how his car can produce more mass in the form of gas than in the fuel consumed. The answer is simple: in his calculation he should include the mass of the oxygen required to burn the fuel. Carbon has an atomic weight of 12 and oxygen 16, so carbon dioxide has a molecular weight of 44.

On this basis I calculate the CO2 production of his car as 228g/km, which is pretty close to the official figure. So we can all be happy: no mass created or destroyed.

Ian Jones, Appleton, Cheshire

PRIUS: THE TRUTH

Scott Brownlee of Toyota is being a bit disingenuous when he claims that the official tests for economy and emissions are “comparable across all cars” (Letters, last week). It would be true to say they are comparable across all cars that use nothing but an on-board fuel supply. But hybrid cars such as the Prius draw a great deal of the energy needed to go through the short test cycle from their fully charged battery, leaving their regular fuel supply untapped for much of the test. In real life, they would have to replenish that energy in the battery by running their internal combustion engine. This would cause their economy to be lower, and their emissions higher, than in the official test cycle.

To make the test figures comparable between hybrids and conventional cars, the hybrids would need to be made to replenish any energy drawn from the battery during the course of the test.

Mike Connally, Reading