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North East Buses Local Bus Scene Bus Operations, Management & Infrastructure
New technology in buses
#11
From:-
(23/03/2014, 02:32)Andreos Constantopolous Wrote: A quick comparison of current Euro6 engines from Volvo http://www.volvobuses.com/bus/na/en-us/_...uage=en-gb
Quote:D5
• 240 hp 900 Nm (also available in biodiesel version)

D8
Three models:
• 280 hp 1050 Nm
• 320 hp 1200 Nm (also available in biodiesel version)
• 350 hp 1400 Nm

D11
Three models:
• 380 hp 1800 Nm
• 430 hp 2050 Nm
• 460 hp 2200 Nm

It's quite easy to see that the larger capacity engines offer higher torques (and, therefore, better 'pulling power'). Higher horsepower will result at the same engine revolutions (power is torque times revolutions).

Two different approaches to the same topic:-

http://www.largiader.com/articles/torque.html

http://www.epi-eng.com/piston_engine_tec...torque.htm

An engine with higher torque is capable of pulling longer gearing ratios, thereby giving the same roadspeed at lower engine revolutions.

The work done is the same (for equivalent roadspeed) but consumption will depend on the comparative economy of the engines at those revolutions.
The smaller capacity engine at higher engine revolutions might well be using more fuel to achieve this - but this will depend on the engine management system.
It is, perhaps, obvious that the components within the smaller capacity engine will 'run further' to achieve the same performance, and, therefore be expected to wear out sooner.

Conversely, if the gearing ratios are the same the larger capacity engine will probably use more fuel (again, depending on the engine management system). Throttle opening position will determine how much fuel is delivered (and how much performance is delivered) so judicious use of the pedal will reduce fuel consumption. A sophisticated 'drive by wire' control could optimise this.
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#12
Notwithstanding the above comments, a hybrid (diesel/electric) system generally involves more 'inefficiencies' (more components each with their own efficiencies) though regenerative braking (where the energy is returned to battery power rather than dissipating it as heat by the brakes) can improve the overall efficiency.

Logically (!) city use with stop/start operation probably better-suits hybrids than sustained high-speed long-distance runs.

Of course the efficiency of the generating component (the power source) is significant. A gas-turbine (as used on the DesignLine vehicles) can be efficient when run at constant speed (as can a suitably specified diesel engine run at optimum (fuel economy) speed).
Attempts in the 1960s (by Ford and Leyland - and Austin in the 1950s) to power road vehicles directly by gas-turbine engines ended in failure due to the fuel consumption of variable-speed operation.
It is the variation in power demand (and, therefore, revolutions) that causes variation in fuel consumption.
A poorly-specified power-source (running constantly at peak power) might be inefficient and 'hungry' for fuel and worse than a simple diesel/mechanical transmission.
Topping-up the traction battery from mains electric will reduce liquid (or gas) consumption and cost will depend on the tariff of the mains electricity used (and might involve additional manpower (and time) to achieve 'refuelling').
Consider the complication of installing a suitable charging point and the time required to charge a simple domestic car that runs solely off electric battery power versus driving to a pump and refuelling liquid (or gas) fuel.
I understand that some gas-powered buses in the region have to be driven significant dead-mileages to access a refuelling point.

The following was gleaned from an overseas source last year (and might not represent current technologies and prices):-
Quote:The resulting economic analysis suggested that procurement of a hybrid bus in lieu of a B12 will deliver a negative economic outcome, with a projected loss of $113,950 (net present value basis) over the life of the vehicle, and a benefit-cost ratio of 0.84.
Compared with a bus fitted with contemporary B7 technology, the economic outcomes are more negative than for the B12, with a projected loss of $313,920 over the life of the vehicle (net present value basis), and a benefit-cost ratio of 0.10.
A sensitivity analysis revealed that the quantum of the above losses would be partly reduced in the face of substantial rises in diesel fuel prices, but the overall economic outcomes would likely remain negative under even more aggressive fuel price rise scenarios.
While the hybrid technology (as trialled) delivered a fuel efficiency benefit of around 15% relative to conventional B12 technologies, this benefit was not sufficient to offset the higher capital cost and ongoing maintenance costs of the hybrid bus. It is estimated that an 88% reduction in the capital cost of the hybrid bus technology would be required to support a break-even investment when compared with a traditional diesel bus operating 70,000 km p.a. over 25 years.
In the case of the more contemporary B7 bus technologies, the hybrid technology (as trialled) was less fuel efficient. This factor, coupled with the higher capital and maintenance costs over a typical bus life, suggests that the B7 currently delivers superior operational, environmental and economic outcomes when compared with hybrid bus technologies.
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#13
(23/03/2014, 07:56)G-CPTN Wrote: From:-
It's quite easy to see that the larger capacity engines offer higher torques (and, therefore, better 'pulling power'). Higher horsepower will result at the same engine revolutions (power is torque times revolutions).

Two different approaches to the same topic:-

http://www.largiader.com/articles/torque.html

http://www.epi-eng.com/piston_engine_tec...torque.htm

An engine with higher torque is capable of pulling longer gearing ratios, thereby giving the same roadspeed at lower engine revolutions.

The work done is the same (for equivalent roadspeed) but consumption will depend on the comparative economy of the engines at those revolutions.
The smaller capacity engine at higher engine revolutions might well be using more fuel to achieve this - but this will depend on the engine management system.
It is, perhaps, obvious that the components within the smaller capacity engine will 'run further' to achieve the same performance, and, therefore be expected to wear out sooner.

Conversely, if the gearing ratios are the same the larger capacity engine will probably use more fuel (again, depending on the engine management system). Throttle opening position will determine how much fuel is delivered (and how much performance is delivered) so judicious use of the pedal will reduce fuel consumption. A sophisticated 'drive by wire' control could optimise this.

240 bhp is quite frankly shocking.
http://www.motortorque.com/guides/buying...dget-17630 - There are some cars with even more bhp than the bus engine! Time for a fleet of taxibuses? Wink

Seriously though, the mid range 8 litre engine, isn't too much different to the current lumps in the B9's.

If the correct bus, is allocated to the correct route - such as a town and city bus as you suggest - in theory, there shouldn't be too many issues.
Stick a 5 litre on a long run and you are asking for problems, no matter how 'economical' or fuel efficient the engine is.
'Illegitimis non carborundum'
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#14
(25/03/2014, 23:57)Andreos Constantopolous Wrote: 240 bhp is quite frankly shocking.
There are some cars with even more bhp than the bus engine!

I realise that your comment was accompanied by a smiley and therefore not confrontational, however for those who didn't notice, the 240 bhp engine in the bus will be operating at half the revolutions per minute that the 240 bhp car engine will need to achieve that figure - so the bus engine torque will be twice that of the car engine.

Think of pushing the bus - the effort (torque) available from the bus engine will be twice that available from the car engine and assisted by the torque converter ratio ( 1.968:1 ) it will be four times that of the car engine.

Power (bhp) indicates the rate at which the effort can be applied - it is defined as the amount of energy consumed per unit time - power is the rate at which this work is performed.
The same amount of work is done when carrying a load up a flight of stairs whether the person carrying it walks or runs, but more power is expended during the running because the work is done in a shorter amount of time.

Agreed that the bus is much heavier than the car, but the gearing compensates for that - though the bus will not accelerate as quickly as the car of course!

It's not that long ago when truck and bus engines of 240 bhp would have been considered 'top of the range', and 140 bhp considered 'adequate' for 24 tons (6 bhp per ton was the maxim)
(OK, maybe that was 40 years ago . . . )
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#15
Video: New Bus Technology Spots Available Seats Upstairs
http://londonist.com/2014/10/video-new-b...stairs.php

Not local, but perhaps something which could come to the North East in the future, should the trial be successful in London...
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#16
(11/10/2014, 21:24)Dan Wrote: Video: New Bus Technology Spots Available Seats Upstairs
http://londonist.com/2014/10/video-new-b...stairs.php

Not local, but perhaps something which could come to the North East in the future, should the trial be successful in London...

Brilliant use of technology.

Many years ago I visited a friend who worked in a university research department.

I enquired what he was working on and he gave me a convoluted explanation - of which I was somewhat sceptical.

Some years later, cameras started appearing on highways, and the Automatic Number Plate Recognition (ANPR) system came into being - exactly what had been described to me!
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#17
(11/10/2014, 21:24)Dan Wrote: Video: New Bus Technology Spots Available Seats Upstairs
http://londonist.com/2014/10/video-new-b...stairs.php

Not local, but perhaps something which could come to the North East in the future, should the trial be successful in London...

Very useful technology for operators to have. Some organisations use similar technology for hot desking and meeting room environments. It allows them to plan their accommodation strategy around demand. If an operator had the ability to see the seat usage capacity for a service all day long, then there's your justification right there for increasing vehicle size or route frequency.
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#18
(11/10/2014, 21:24)Dan Wrote: Video: New Bus Technology Spots Available Seats Upstairs
http://londonist.com/2014/10/video-new-b...stairs.php

Not local, but perhaps something which could come to the North East in the future, should the trial be successful in London...

Sounds a good idea, hopefully its a success 
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#19
For those interested in what the eFan Micro Hybrid System involves, it simply replaces the hydraulically-driven cooling fan (and the combined water/air intake charge cooler) with electrically-powered cooling fans working on separate air-charge cooler and water radiator.

In simple terms, it replaces the drag required to constantly power the hydraulic fan from 20 kW to 3 kW with electric fans that can be switched on and off as required. This will reduce the fuel consumption.

Quote:On a conventional hydraulically driven fan system, air is sucked from the outside of the bus through a charge air cooler with a hydraulic oil cooler alongside and then through a jacketed water filled radiator by a large fan driven by a hydraulic motor and controlled by a hydraulic control valve. AVID say this method traps debris within the system making it less effective. The debris becomes difficult to remove and the radiators are easy to damage. The system is also prone to hydraulic leaks.

With the AVID eFan micro hybrid system, air flows through a bank of high performance brushless DC electric fans, cooling a charge air cooler and a water radiator. There are usually six fans, four cooling the water system and two the charge air. Cooling the charge air cooler and the water radiator independently enables their temperatures to be more accurately controlled. The electric fans used are units specially designed for vehicle applications delivering 50% more airflow than the most efficient similarly sized units available commercially. They can be run in reverse, effectively as powerful blowers, to remove accumulated debris and keep the system running cleanly and efficiently. There is no hydraulic system so it can’t leak and doesn’t need cooling.
The system is controlled by an electronic controller connected to the vehicle’s CANbus system. It monitors the water temperature through a sensor in the radiator inlet and the charge air temperature through a sensor in the charge air cooler outlet. There are three functions available to the maintenance team on each system, a reversing switch that enables the fans to be run as blowers, a diagnostic connector port and a diagnostic lamp button.
A major difference between the hydraulic and electric systems is the energy required. When operating at full capacity, the eFan uses 3kW compared with a figure of around 20kW for a hydraulic system. On top of this, it only runs when needed and switches itself off when it isn’t. This ensures that engines operate at their optimum running temperature and also, because the fans do not operate when they are not needed in the early stages of a vehicle’s duty cycle, reduces the warm up time.
The absence of hydraulic fluid is a significant safety factor because, they claim, it is often a hydraulic problem that will start an engine bay fire or exacerbate one started in another way.
Another benefit from fitting an eFan is a reduction in problems with diesel particulate filters (DPFs).  This is because additional soot is created when engines are not running sufficiently hot to optimise combustion. This soot collects in the DPF and the exhaust temperature is often not high enough to burn it off. As the eFan helps keep the engine running at its best temperature, less soot is created.
In more extreme cases of overcooling, it can be that overcooled coolant is released into the engine by the thermostat creating thermal shock which damages the power unit. Only running the fan when it is needed makes overcooling less likely and reduces instances of thermal shock.
Elucidating on the benefits of the eFan, typically, a bus radiator is designed to last a couple of years at most but the eFan is designed to last at least ten years and was essentially a fit and forget type system. A robust technology called bar and plate was used because, while the traditional tube and fin construction method was OK on trucks, it was less durable in bus applications. The eFan is designed to be robust for bus applications, which was hard. Although the eFan is more durable it is not heavier. The complete pack weighs 60-70Kg which is comparable to a conventional hydraulic pack. ‘We don’t have a heavy hydraulic fan and supporting framework,’ said Chris, adding, ‘because of this there is less vibration and less noise.’
Noise is increasingly important and here there are advantages to the eFan in two more respects. Firstly, there is a kerbside quiet feature that has been developed whereby at below 5kmh, the noise output is reduced through an algorithm that prevents overcooling. Secondly, and of local benefit to operators with residential neighbours, is the low start up noise characteristic that it gives a bus because the eFan does not activate as soon as it is turned on, only when the engine reaches a temperature at which it needs cooling. It is also quieter because it runs for less of the time.
An advantage that becomes increasingly important as space becomes ever more at a premium within the bus envelope, is the eFan’s packaging attributes. ‘We can split the charge air from the water and have the relevant components in different locations, which is far more difficult to do with a belt or hydraulic driven system. Also, with one big fan you have to have a big square heat exchanger but with our smaller multiple eFans you can have virtually any shape of heat exchanger.’

From:- http://www.busandcoachbuyer.com/avid-tec...ro-hybrid/

(with photographs of the components)
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#20
I've been trying to discover the technical details of Wrightbus's 'micro-hybrid' system, but the best I have managed is:-

Quote:Micro Hybrid technology captures the energy generated from a bus’s braking system, and redistributes this energy to power pneumatics, hydraulic and electrical systems which would otherwise require power from the engine.
The result is a reduction in fuel consumption of up to 10%, leading to substantial savings over a bus’s typical 15-year operational service life.
Quote:the Micro Hybrid equipment – which charges the batteries during braking to power auxiliaries – deliver a significant fuel saving, it also entitles the operator to enhanced BSOG payments without the extra costs associated with a full hybrid’s complexity and batteries.
Quote:StreetLite Micro Hybrid range has achieved Low Carbon Emission Bus Certification. The StreetLite Micro Hybrid is a very low cost hybrid system that allows the bus to recuperate lost braking energy to power the vehicle electrics and the vehicle compressed air system for free. This improves fuel efficiency by approximately 10% on a typical city bus drive cycle.
Quote:The StreetLite Micro Hybrid uses the same engine, transmission and rear axle as the conventional StreetLite, but re-jigs the auxiliary systems to give the vehicle smart control of energy generation and usage on the vehicle.
A standard bus driveline has three important extra bits powered by the engine:
1. Air compressor (for brakes) which runs when the air tank pressure is below a given set point
2. Alternator (to charge battery and power lights etc.) which runs continually with a load proportional to the electrical load on the bus
3. Hydraulic pump for cooling fan (to stop the bus melting) which runs continually with a load proportional to engine speed.


Now in the Micro Hybrid, when the driver presses the brake pedal, some of the waste energy is stored in compressed air tanks and the compressor only runs when really, really needed (which is hardly ever on a busy stop-go city route - lots of brake presses.
Likewise with the alternator, but here the spare energy is stored in the batteries. Again the alternator is hardly ever used on a busy city service. The hydraulic pump becomes an electric pump, again running only when needed.
In this way, the load on the engine is significantly reduced, and the auxiliary systems are powered by waste energy that would otherwise be lost. This has the additional benefit of reducing the load on the retarder and brakes, which will also reduce the load on the cooling pack and extend the life of the friction brakes. The overall efficiency gain when Micro Hybrid is added to a conventional StreetLite is around 9.2% and this additional fuel saving is enough to place the vehicle comfortably below the threshold for Low Carbon Emission Bus Certification.
Quote:Wrightbus’ “Micro Hybrid” recovers braking energy, but rather than use it to directly benefit propulsion as in full hybrid systems, this energy is stored in storage systems already on board and is used to power pneumatics, hydraulics and electrical items. These components would otherwise require power from the engine and, by using the energy harvested from the braking system, reduces overall fuel consumption by around 10%.

Forgive me, but there's nothing there that explains to me exactly how these savings are achieved - ie what device does what - maybe it's that the hydraulic pump is now electrically driven - and the alternator does what?

I've read that the system uses the standard vehicle batteries (so there is no added storage equipment), but when a battery is fully-charged there's not much else you can do with electricity - other than use it to drive electric pumps - and the system is said to harvest energy during braking (so we aren't talking about an engine-driven generator - maybe it is driven from the gearbox retarder?)

It seems to me to be smoke and mirrors - but that is only because I haven't found a plausible technical explanation yet despite extensive searching . . .

You would think that for a pioneering system that there would be a treatise published explaining exactly how the saving is achieved - but maybe they don't want the competition to cotton on?
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