Proposed London low emission zone.

All petrol cars with an ECU and a catalytic converter will have a sensor near the cat, but an engine under load will consume more fuel than one that is idling or at a constant speed.

My Astra has an instant fuel consumption display, and when accelerating away from rest the consumption can easily drop to less than 10 mpg. This must result in a corresponding increase in pollution.

At a steady speed between 40 and 60 mph it will show between 40 and 45 mpg, and over 100 mpg on overrun. When going downhill it will show 999 mpg, so almost nothing being produced.

Central heating boilers by their nature are designed for long(-ish) efficient burns. Even a modulating boiler will (hopefully) only gradually ramp up power.

Only committed diesel-heads will constantly try and deflect blame onto ships in the middle of the pacific, or gas boilers for high NO2 pollution in many town centres, but its a numbers issue. There are now well over 10 million cars with diesel engines and the road tax bribe has to be main culprit. How many of these cars only do a few thousand miles a year, to the supermarket, garden centre or vets, clogging up their DPF in the process ?.

But this low emission zone isn't about CO2. It is that which made diesels so popular with some badly advised civil servants, a couple of years ago. It's about poisonous emissions, NOX, CO etc.

If CO2 were the main issue it would be based on engine size - not age.

Or removal of clots who need to be slowed down by speed bumps.

Many are now modulating. All combi boilers modulate the output to control the hot water temperature. Combi boilers have much higher output than regular CH boiler as they have to supply the full multipoint hot water load. Regular CH heats the hot water in the tank over a much longer time. Problem is unless used promptly stored hot water goes cold and all the heat is wasted.

Then there is the problem with quenched combustion. On start up the heat exchanger is cold, burning gas hits this, combustion ceases with incomplete products. Makes all sorts of nasty NOx and even formaldehyde.

Condensing boilers have much lower heat exchanger temperature as flow and return should be 60/40°C instead of 79-82/-11°C. Condensing boilers are close to 100% efficient and with cold water feed can be over 100% as they act as air source heat exchanger. (gas boiler efficiency is calculated on gas heat input and ignoring fan electrical input). Conventional boilers are at best 80% efficient and have installation efficiency around 70%.

There has been a huge campaign to increase installed boiler efficiency resulting in lots of "condensing combis" being installed.

The real truth is they have burnt all of our domestic "high speed gas" (remember those ads in the 60's and 70's) in closed cycle gas turbine generators and are now having to import 40% of the supply.

Or implementation of the more expensive option developed many years ago

- a hollow, rubber speed-bump, that when hit by a vehicle travelling at or below the speed limit deflates, giving a bump-free ride, but when hit by a faster vehicle, the escaping air is travelling faster and closes the exhaust valves, thus giving a hard jolt. Affect only the speeders and stop the rest of us having to slow to a quarter of the speed limit to comfortably cross.

SteveW

Still messy and would require regular maintenance. There are also the signs that light up and indicates your speed. OK, so people tend to slow down for those, them immediately speed up. But at least they seem have some calming effect more than if they were not there. This is because some of the drivers then stick to that limit after passing the sign, thereby creating the bottleneck for those who want to speed :) I've seen this many times.

Be interesting to know the cost of installing those. And maintaining them. Given they can't afford to fill in potholes.

Most of them round here, or rather the ones still working, are set to start warning you're going too fast well below the actual limit. So cry wolf too often. The one I go past most often starts flashing at 20mph, in a 30 limit. And on a wide main road.

My latest Mot for an 08 1.6 Petrol engine was CO 0.023 and HC 45

(short drive before, engine oil temperature measurement bypassed)

In message , "Dave Plowman (News)" writes

Like the Congestion Charge, I'm still convinced that the Low Emission Charge is all about extracting £££££££££££ from the unfortunates who need to use their vehicles to enter London.

Enter London? How about those who live there?

Quite sure raising money is the major part, though.