Who's right(er) here?
Discussion
Here's an exchange on another (cycling - sorry 
) Forum. I'm one of the posters. I've not got a huge amount of technical knowledge, but I think I have a fair lay petrolhead's grasp of the issues. I think that the other poster is being extremely selective in his post. What do you think?
His post on a thread
I was in London on Monday, first time in years, to see Kate Bush(totally stunning BTW) and I found I was having difficulty breathing while walking so how people ride down there beats me. Maybe you adapt to the lack of oxygen in the same way Sherpas have.
Me
It has been particularly bad this week. Diesel vehicles are big contributors. This can't come too soon: http://www.bbc.co.uk/news/uk-england-london-285402...
He
Oh yes petrol has green pumps therefore good, but diesel black pumps therefore bad.
I suspect the real reason for the charge is the loss of tax revenue that results in the use of diesel fuel. Both fuels pollute but I happen to find that it's fumes from petrol engines that can make my chest tighten not diesel fumes even though they are unpleasant.
Me
I have no idea what the motivation is, but not particularly useful to get into that, or respond to "black pump bad green pump good" with rolleyes, which wasn't a point I was making.
Diesel is, by and large, an unsuitable fuel for use in urban areas such as London. Many journeys are short. Engines do not warm, the Euro 5/6 emissions gubbins does not warm sufficiently to do its job (and cars break down as a result, and are often as consumptive as their petrol equivalents - but that's another discussion) so carcinogenic particulates are put into the atmosphere in significant quantities. The results can be seen, felt and indeed tasted in conditions such as last week's.
He
As I said petrol is far worse as far as I'm concerned. Petrol engines warm up slowly and this is when most of the pollution is produced.
A diesel engine works by compressing a cylinder (or more for a turbo) full of air to a high temperature to ignite the injected fuel. If this temperature is insufficient it won't run - simple as that - there's nothing else to ignite the fuel. This means the combustion chamber is hot from the time the engine starts - it has to be.
A petrol engine works by igniting an explosive mixture of petrol vapour and air. The combustion chamber temperature is unimportant (within limits) for this to occur. Therefore a petrol engine can run with a cool combustion chamber, which also means there tends to be incomplete combustion as well, resulting in a whole range of emissions. The combustion chamber can therefore warm much slower especially if idling. Before catalytic converters were universal, it was noticeable that petrol engine exhausts would show water vapour condensate for longer periods of time than diesel counterparts as the exhaust gases are cooler.
Idling of petrol engines can also result in incomplete combustion, because there is insufficient air intake - hence one need for catalytic converters for them - whereas idling diesel engines can result in effectively complete combustion because there is excess air.
Welcome your thoughts
) Forum. I'm one of the posters. I've not got a huge amount of technical knowledge, but I think I have a fair lay petrolhead's grasp of the issues. I think that the other poster is being extremely selective in his post. What do you think?His post on a thread
I was in London on Monday, first time in years, to see Kate Bush(totally stunning BTW) and I found I was having difficulty breathing while walking so how people ride down there beats me. Maybe you adapt to the lack of oxygen in the same way Sherpas have.
Me
It has been particularly bad this week. Diesel vehicles are big contributors. This can't come too soon: http://www.bbc.co.uk/news/uk-england-london-285402...
He
Oh yes petrol has green pumps therefore good, but diesel black pumps therefore bad.
I suspect the real reason for the charge is the loss of tax revenue that results in the use of diesel fuel. Both fuels pollute but I happen to find that it's fumes from petrol engines that can make my chest tighten not diesel fumes even though they are unpleasant.
Me
I have no idea what the motivation is, but not particularly useful to get into that, or respond to "black pump bad green pump good" with rolleyes, which wasn't a point I was making.
Diesel is, by and large, an unsuitable fuel for use in urban areas such as London. Many journeys are short. Engines do not warm, the Euro 5/6 emissions gubbins does not warm sufficiently to do its job (and cars break down as a result, and are often as consumptive as their petrol equivalents - but that's another discussion) so carcinogenic particulates are put into the atmosphere in significant quantities. The results can be seen, felt and indeed tasted in conditions such as last week's.
He
As I said petrol is far worse as far as I'm concerned. Petrol engines warm up slowly and this is when most of the pollution is produced.
A diesel engine works by compressing a cylinder (or more for a turbo) full of air to a high temperature to ignite the injected fuel. If this temperature is insufficient it won't run - simple as that - there's nothing else to ignite the fuel. This means the combustion chamber is hot from the time the engine starts - it has to be.
A petrol engine works by igniting an explosive mixture of petrol vapour and air. The combustion chamber temperature is unimportant (within limits) for this to occur. Therefore a petrol engine can run with a cool combustion chamber, which also means there tends to be incomplete combustion as well, resulting in a whole range of emissions. The combustion chamber can therefore warm much slower especially if idling. Before catalytic converters were universal, it was noticeable that petrol engine exhausts would show water vapour condensate for longer periods of time than diesel counterparts as the exhaust gases are cooler.
Idling of petrol engines can also result in incomplete combustion, because there is insufficient air intake - hence one need for catalytic converters for them - whereas idling diesel engines can result in effectively complete combustion because there is excess air.
Welcome your thoughts
Bonefish Blues said:
Here's an exchange on another (cycling - sorry ) Forum. I'm one of the posters. I've not got a huge amount of technical knowledge, but I think I have a fair lay petrolhead's grasp of the issues. I think that the other poster is being extremely selective in his post. What do you think?
His post on a thread
I was in London on Monday, first time in years, to see Kate Bush(totally stunning BTW) and I found I was having difficulty breathing while walking so how people ride down there beats me. Maybe you adapt to the lack of oxygen in the same way Sherpas have.
Me
It has been particularly bad this week. Diesel vehicles are big contributors. This can't come too soon: http://www.bbc.co.uk/news/uk-england-london-285402...
He
Oh yes petrol has green pumps therefore good, but diesel black pumps therefore bad.
I suspect the real reason for the charge is the loss of tax revenue that results in the use of diesel fuel. Both fuels pollute but I happen to find that it's fumes from petrol engines that can make my chest tighten not diesel fumes even though they are unpleasant.
Me
I have no idea what the motivation is, but not particularly useful to get into that, or respond to "black pump bad green pump good" with rolleyes, which wasn't a point I was making.
Diesel is, by and large, an unsuitable fuel for use in urban areas such as London. Many journeys are short. Engines do not warm, the Euro 5/6 emissions gubbins does not warm sufficiently to do its job (and cars break down as a result, and are often as consumptive as their petrol equivalents - but that's another discussion) so carcinogenic particulates are put into the atmosphere in significant quantities. The results can be seen, felt and indeed tasted in conditions such as last week's.
He
As I said petrol is far worse as far as I'm concerned. Petrol engines warm up slowly and this is when most of the pollution is produced.
A diesel engine works by compressing a cylinder (or more for a turbo) full of air to a high temperature to ignite the injected fuel. If this temperature is insufficient it won't run - simple as that - there's nothing else to ignite the fuel. This means the combustion chamber is hot from the time the engine starts - it has to be.
A petrol engine works by igniting an explosive mixture of petrol vapour and air. The combustion chamber temperature is unimportant (within limits) for this to occur. Therefore a petrol engine can run with a cool combustion chamber, which also means there tends to be incomplete combustion as well, resulting in a whole range of emissions. The combustion chamber can therefore warm much slower especially if idling. Before catalytic converters were universal, it was noticeable that petrol engine exhausts would show water vapour condensate for longer periods of time than diesel counterparts as the exhaust gases are cooler.
Idling of petrol engines can also result in incomplete combustion, because there is insufficient air intake - hence one need for catalytic converters for them - whereas idling diesel engines can result in effectively complete combustion because there is excess air.
Welcome your thoughts
"Idling of petrol engines can also result in incomplete combustion, because there is insufficient air intake - hence one need for catalytic converters for them - whereas idling diesel engines can result in effectively complete combustion because there is excess air" ) Forum. I'm one of the posters. I've not got a huge amount of technical knowledge, but I think I have a fair lay petrolhead's grasp of the issues. I think that the other poster is being extremely selective in his post. What do you think?His post on a thread
I was in London on Monday, first time in years, to see Kate Bush(totally stunning BTW) and I found I was having difficulty breathing while walking so how people ride down there beats me. Maybe you adapt to the lack of oxygen in the same way Sherpas have.
Me
It has been particularly bad this week. Diesel vehicles are big contributors. This can't come too soon: http://www.bbc.co.uk/news/uk-england-london-285402...
He
Oh yes petrol has green pumps therefore good, but diesel black pumps therefore bad.
I suspect the real reason for the charge is the loss of tax revenue that results in the use of diesel fuel. Both fuels pollute but I happen to find that it's fumes from petrol engines that can make my chest tighten not diesel fumes even though they are unpleasant.
Me
I have no idea what the motivation is, but not particularly useful to get into that, or respond to "black pump bad green pump good" with rolleyes, which wasn't a point I was making.
Diesel is, by and large, an unsuitable fuel for use in urban areas such as London. Many journeys are short. Engines do not warm, the Euro 5/6 emissions gubbins does not warm sufficiently to do its job (and cars break down as a result, and are often as consumptive as their petrol equivalents - but that's another discussion) so carcinogenic particulates are put into the atmosphere in significant quantities. The results can be seen, felt and indeed tasted in conditions such as last week's.
He
As I said petrol is far worse as far as I'm concerned. Petrol engines warm up slowly and this is when most of the pollution is produced.
A diesel engine works by compressing a cylinder (or more for a turbo) full of air to a high temperature to ignite the injected fuel. If this temperature is insufficient it won't run - simple as that - there's nothing else to ignite the fuel. This means the combustion chamber is hot from the time the engine starts - it has to be.
A petrol engine works by igniting an explosive mixture of petrol vapour and air. The combustion chamber temperature is unimportant (within limits) for this to occur. Therefore a petrol engine can run with a cool combustion chamber, which also means there tends to be incomplete combustion as well, resulting in a whole range of emissions. The combustion chamber can therefore warm much slower especially if idling. Before catalytic converters were universal, it was noticeable that petrol engine exhausts would show water vapour condensate for longer periods of time than diesel counterparts as the exhaust gases are cooler.
Idling of petrol engines can also result in incomplete combustion, because there is insufficient air intake - hence one need for catalytic converters for them - whereas idling diesel engines can result in effectively complete combustion because there is excess air.
Welcome your thoughts
That's utter rubbish.
They are both inefficient and dirty when cold, the opposite when up to operating temperature.
Diesel cars are being phased out completely because it is impossible to make them clean and efficient at the same time.
226bhp said:
Diesel cars are being phased out completely because it is impossible to make them clean and efficient at the same time.
Don't know where you heard that, there are more than ever on the roads today.Just do a search for pretty much any car on autotrader then see the split between diesel & petrol.
Many have more diesel than petrol, even as few as 5 years ago the opposite was true.
andyiley said:
226bhp said:
Diesel cars are being phased out completely because it is impossible to make them clean and efficient at the same time.
Don't know where you heard that, there are more than ever on the roads today.Just do a search for pretty much any car on autotrader then see the split between diesel & petrol.
Many have more diesel than petrol, even as few as 5 years ago the opposite was true.
Bonefish Blues said:
Am I right in sying that petrol engines warm up more quickly because they are less thermodynamically efficient than diesels, so produce more "waste heat" - leaving aside the larger heavier block an ancillaries to warm.
I believe so. I have heard it said you can leave a diesel idling for hours when started from cold and it won't reach operating temperature. No idea if that is true or not.The reason...it's another money making scam from the government of course. They see diesels being more commonplace in the city...so lets hit them with another tax
But yes diesels are dirty old things, who's pollutants are more harmful than petrol
Now if they were serious about cleaner engines and fuel...they'd give some proper support to LPG or E85 etc.
But nope...they dont. That surely speaks volumes about their intentions
But yes diesels are dirty old things, who's pollutants are more harmful than petrol
Now if they were serious about cleaner engines and fuel...they'd give some proper support to LPG or E85 etc.
But nope...they dont. That surely speaks volumes about their intentions
A downside of the better thermal efficiency of the diesel.I went back with:
I don't agree with several of the points you make, I'm afraid.
Both engines are dirty until up to full operating temperature. Just because a diesel runs doesn't mean it's up to its optimum temperature for full combustion.
The converse is the case v-a-v warm-up cycle for the two engine types.
Petrol engines warm more quickly than diesel due to their lower thermal efficiency (25-30% vs 40%) which yields more "spare" energy as heat to warm block, coolant, oil & cat. Diesels warm more slowly for this reason, and also because their block and cooling system is necessarily more massive.
I cannot understand the point about an idling petrol engine not having sufficient air for complete combustion. They can get plenty of oxygen for combustion, as can diesels.
If that were the case how could car engines without significant ram air effect (which most road engine installations don't have) possibly operate at say 5K revs when their oxygen needs are massively greater?
Catalytic converters are there because no engine converts all its fuel into energy. A hot cat. is a very effective way of removing unburnt hydrocarbons and other potentially harmful emissions. A hot DPF is an effective way of burning particulates. Note each must be hot to work properly (or at all in the case of the DPF). That's why I made the specific point about the effect of diesel engines, with their longer warm-up cycle and non-functioning DPFs in urban areas.
It's also the case that the development of diesels seems to have reached a plateau, with manufacturers now turning back to petrol/hybrids/electric in the search for lower emissions to meet ever-tighter Regulations.
Where we do agree is that notwithstanding technical development of both types, both are polluting!
I don't agree with several of the points you make, I'm afraid.
Both engines are dirty until up to full operating temperature. Just because a diesel runs doesn't mean it's up to its optimum temperature for full combustion.
The converse is the case v-a-v warm-up cycle for the two engine types.
Petrol engines warm more quickly than diesel due to their lower thermal efficiency (25-30% vs 40%) which yields more "spare" energy as heat to warm block, coolant, oil & cat. Diesels warm more slowly for this reason, and also because their block and cooling system is necessarily more massive.
I cannot understand the point about an idling petrol engine not having sufficient air for complete combustion. They can get plenty of oxygen for combustion, as can diesels.
If that were the case how could car engines without significant ram air effect (which most road engine installations don't have) possibly operate at say 5K revs when their oxygen needs are massively greater?
Catalytic converters are there because no engine converts all its fuel into energy. A hot cat. is a very effective way of removing unburnt hydrocarbons and other potentially harmful emissions. A hot DPF is an effective way of burning particulates. Note each must be hot to work properly (or at all in the case of the DPF). That's why I made the specific point about the effect of diesel engines, with their longer warm-up cycle and non-functioning DPFs in urban areas.
It's also the case that the development of diesels seems to have reached a plateau, with manufacturers now turning back to petrol/hybrids/electric in the search for lower emissions to meet ever-tighter Regulations.
Where we do agree is that notwithstanding technical development of both types, both are polluting!
His post on a thread
I was in London on Monday, first time in years, to see Kate Bush(totally stunning BTW) and I found I was having difficulty breathing while walking so how people ride down there beats me. Maybe you adapt to the lack of oxygen in the same way Sherpas have.
Most Sherpas were diesel weren't they?
I was in London on Monday, first time in years, to see Kate Bush(totally stunning BTW) and I found I was having difficulty breathing while walking so how people ride down there beats me. Maybe you adapt to the lack of oxygen in the same way Sherpas have.
Most Sherpas were diesel weren't they?
He complained about the quality of air in London.
You blamed diesel engines.
He doesn't like petrol engines.
Kate Bush is in there too.
There is now a debate about... well... maybe... thermal efficiency, or maybe operating temperature, or maybe exhaust after-treatment, or maybe taxation, or maybe thermal mass, or...
It's a pointless thread that's going nowhere, drop out of it and save your sanity.
You blamed diesel engines.
He doesn't like petrol engines.
Kate Bush is in there too.
There is now a debate about... well... maybe... thermal efficiency, or maybe operating temperature, or maybe exhaust after-treatment, or maybe taxation, or maybe thermal mass, or...
It's a pointless thread that's going nowhere, drop out of it and save your sanity.
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