| Author | Message | ||
     Peter Colwell Experienced User Username: peter_colwell Post Number: 30 Registered: 3-2005 |
Most of us are aware that we are custodians of our cars for the time being, and that the cars now in the hands of genuine enthusiasts will endure beyond the lifetime of their current owner. However, as we die out, there is something else dying out as well. Basic mechanical knowledge. The increasing popularity of diesel engined cars in Australia, has exposed the extreme lack of knowledge of what makes engines tick, how they work, and what makes one different from another. This point was driven home recently when a question was asked of a newspaper moto-journalist; "What is the difference between horsepower and torque?" Instead of the very simple correct answer, the journalist blathered on, confusing himself and everyone else. He did not know. In another place, an advertisement for a diesel car extols the virtues if its "fuel-injected diesel engine...", as though there was some other kind. Another makes much of the electric Toyota Prius' very high torque. Somebody needs to tell him that electric motors (and steam engines) develop their greatest torque at stall, when they are not turning at all, and consequently are producing zero power. The biggest true technical advance in recent times has been the advent of the holy grail; direct fuel injection in a petrol engine. But I fear that the real benefit will be lost in the confusion and fog. The connection of this subject with Rolls-Royce for me, is that the older RR engines in particular are such a unique design, combining a very heavy flywheel design with near perfect balance. The result being the uniquely quiet and vibration-free running. Peter | ||
| bob uk Unregistered guest Posted From: brig-cache-4.server.ntli.net |
Rolls-Royce are not the only engine maker who uses heavy flywheels to absorb vibs. Heavy flywheels mean that the engine will be slow to accelerate and slow to de-accelerate which can give gear changing problems on manual gearboxes. It is not possible to make a six cylinder engine with perfect balance. V8 with a 90 degree crank will balance out. So a heavy flywheel is not necessary. Direct petrol injection really comes into its own when the engine is super or turbo charged. Turbo charged diesel engines have valve timming that allows more valve overlap so that the pressure of the turbo blows air though the cylinder. If this is done with a petrol engine without direct injection petrol will be blown down the exhaust system. By injecting the petrol into the cylinder after the valves are closed allows lots of blow through and complete cleansing of the cylinder. Power is torque in a time period. In other words torque is foot pounds and power is foot pounds with a time element. In imperial measurement the foot pounds will equal the bhp when the engine is reving at 5252 revs. All graphs showing torque and bhp will meet at 5252 rpm. To get more power all that is needed is more revs assuming that the torque holds out. My Shadow engine has about 200 bhp at 4500 rpm if the engine could rev to say 5500 rpm and the torque held out then is would produce maybe another 50 bhp. Modern superbikes such as the Honda Fireblade rev to about 10,000 rpm and produce 130 BHP if the engine was to rev only 5000 rpm then it would only have 65 bhp. I see lots of errors in the press regarding motor vehicles. And some of the worse offenders are the motor manuafacturers themselves. They rely on the public ignorance to get away with it. I think that time will show that hybrid cars with both electric and infernal combustion engines are not ae good as they are made out to be. Already I am hearing that the Prius does not do the MPG that is claimed. One was road tested 500 miles at 70 mph on motorways and it gave 45 mpg which is no better than a deisel. What happens when the batteries wear out. I can see a time when the car will be scrapped because the batteries need replacing, plus when the car is worn out there will be a disposal problem because of the giant lead acid batteries (Message approved by david_gore) | ||
| Jon Rothwell Frequent User Username: jon_rothwell Post Number: 41 Registered: 4-2004 |
There is a real problem with lack of mechanical knowledge even among todays "Auto Technicians", oddly enough many of them also lack the basic electronic skills needed with todays vehicles. It is still possible for someone with experience in mechanics and electronics to maintain and repair most cars (new and old) at home, but it takes real effort and I suspect that due to the advent of the almost "disposable" car in future this will be left to the real automotive enthisiasts. Older classic car owners will have real problems in a few years as the older generations of real mechanics retire. As a matter of interest the Prius uses "thirty-eight Nickel-Metal Hydride (Ni-MH) cells, giving a total of 273.6 volts" to quote the Australian publication Autospeed. I believe the battery pack life is in excess of 5 years, but it will be expensive to replace and dispose of and this extra cost needs to be factored into any fuel savings over the life of the vehicle. | ||
| bob uk Unregistered guest Posted From: brig-cache-4.server.ntli.net |
A five year battery life will mean that the Prius maybe scrap after five years. The value of a car after 5 year is about a third of its new price. However the value of car that was too expensive in the first place could devalue even more. Factor in the potental of expensive battery failure which after 5 years will not be covered by any warantee will make buyers wary of second hand ones. This will make a 5 year Prius hard to sell and hence cheap(er) Most people are willing to go green providing it is affordable ( I am being polite because most will want it as cheap as possible ) Also when running on petrol the Prius will be dragging weight of the batteries around which goes someway into explaining the slugish accelaration and the fuel ecomony. I can foresee a time when a car will have a fuel cell which runs for say 100,000 miles and then the car is recycled. Fuel is put in when the car is made and when it runs out the car is recycled. In Europe we are moving towards making the original maker of the car responsible when the car is scrapped. I reckon that eventually cars will not be sold only rented and the makers will take the car away after say 3 years and recycle it. Modifications will not be allowed- not even a different radio. The internal combustion engine has a very good power to weight ratio until battery technology can near equal this I see electric vehicles as second best. The electric motor as previously stated produces most of its torque when stalled which is ideal for a car. In London up until the 1960's we had Electric trolley buses which ran off of overhead wires like a tram. These were quite fast and had governors to stop the driver accelerating to fast from rest and throwing the passengers off the open platform at the back. One of the worse things London did was to replace them with Deisel buses. I never quite understood why because at the time London used to get pea souper fogs which lasted for days and killed many who had chest complaints such as asthma. I remember these fogs and I used to walk home from school and remember to turn left at the white double gates else I would get lost, it was that bad. (Message approved by david_gore) | ||
| David Gore Moderator Username: david_gore Post Number: 685 Registered: 4-2003 |
Hi Bob, If my memory is still valid, I seem to remember the London "pea soup" fogs were largely cause by the large number of open fires still being used for winter heating. The enforced use of "smokeless" fuel in open fires and gas boilers for central heating reportedly brought a dramatic reduction in fogs in the 1960's. The replacement of electric trams and trolley buses with diesel buses is a particular obsession of mine. A good friend [now deceased] was a senior manager in the NSW Department of Transport Tramway sysytem at the time and told me 20 years later of the involvement of certain UK and USA diesel engine, bus chassis and tyre manufacturers in having the NSW Government abandon their electric traction system in favour of diesel buses. The circumstances associated with this decision did not enhance the reputation of those involved and has been kept hidden since. Tram tracks in high-traffic areas were being placed in concrete and trams were being given major rebuilds less than 3 weeks before the decision to scrap the system in its entirety was announced. The Victorian government thought logically about their public transport system and have kept their trams right up to the present despite the later problems with privatisation. You only have to ride in a Melbourne tram and a Sydney bus to see which is the better form of public transport. Unless there is a major technological breakthrough in the immediate future, I believe the hydrogen fuel cell and electric traction will power our Rolls-Royce and Bentley vehicles in the not-too-distant future. I do not see any future in the use of hybrids and batteries but greater use of conventional internal combustion engines using LPG or bio-diesel as fuel. I think we will see a new-generation turbo-diesel in both R-R & B vehicles a lot earlier than we anticipate. | ||
| Peter Colwell Experienced User Username: peter_colwell Post Number: 33 Registered: 3-2005 |
I agree that hybrid petrol/electric vehicles will not be the way of the future. They sound good to people unfamiliar with the downside of batteries. But given the incredible pace of development of the petrol engine, I think it has some way to go yet. The oil scare of the seventies promoted the use of electronic controls, which has seen amazing advances in both power from fuel used, smoothness, and reduction of pollution. The diesel principle is inherently more efficient, but a lot of the power produced by diesels is actually used in overcoming internal resistance, in driving itself, something like 70% I think. Eg. overcoming the 20 to one compression ratios. What that means is a diesel producing a free 100HP has to be built to the engineering standard of a 330HP engine. Diesels have to be designed stronger to withstand the huge internal forces. And built to extremely fine tolerances. They are best suited to semi-industrial use. I know that the modern light diesels of today, like the BMW 3 litre, are amazing, but they still have to built to withstand the huge inertial forces, = high cost. The cost of repairing a poorly maintained diesel will exceed the value of the vehicle in some cases of small cars. In the context of this forum, one wonders how our descendants will go about restoring a 2006 Rolls-Royce Phantom in 2050, which has defunct electronic systems.... PS, I think that the electric trolley buses are still used in Wellington New Zealand. At least they were not long ago. | ||
| bob uk Unregistered guest Posted From: brig-cache-4.server.ntli.net |
I agree I think the present passenger car diesel engines being made are good enough to power a Rolls-Royce. VW has a 4 Litre V8 diesel that is quite good. This engine could be enlarged a bit to give more midrange torque say 6 litres. The problem that has stopped diesels in the past is diesel knock. When the engine is reving a bit this goes. I have heard some really smooth diesels that belie that are diesels until the engine rev drops to idle and then we get the clatter. Common rail technology stops this -- almost. When fuel is squirted into the cylinder at first is does not burn then all of a sudden it explodes and the rest of fuel is squirting in and burning as it leaves the nozzle. As the revs increase the peroid of squirting shortens and the piston is moving faster so when the explosion happens the piston is moving away from the explosion and the explosion turns into controlled burning and a quieter engine. Common rail squirts a small amount fuel in first to start the fire and then the rest after a short delay. This stops diesel knock. Very recntly bosch has done a load more work and the injection pressures are higher and therefore faster. fast means more fuel can be burnt and this means more torque and therefore more power and more revs because the fuel system can keep pace. more revs lead to even more power. There is a Skoda hatch back which is diesel and is as fast as a VW GTi. 10 years ago 50 BHP per litre from a petrol engine was consided good modern car diesels are easily exceeding that. Check out Peugeot's HDi 2.2 litre engine it has a big wallop of midrange torque which makes the smaller cars it is fitted to very quick for a family car. (Message approved by david_gore) |
