Diesel Hybrid

[Billy_BAD_Boy]

Originally Posted by euromodder

Like the 230mpg for the Volt.
And probably calculated in a similar way to make it look good.

You are reading my thoughts friend.

@Arragonis only time will tell! But I am sure for the success of diesel hybrids ... at least in Europe

[bwilson4web]

Originally Posted by Arragonis

Again I wonder about the benefits of Diesel + Hybrid vs smaller and more powerful Diesel.

I'll try to give an answer with these assumptions whose ratios somewhat match the parameters of the 1.5L/1.8L Prius:

1. smaller diesel 50 kW, ordinary transmission 0 kW
2. smaller diesel 50 kW, hybrid transmission 50 kW for 5 minutes
3. larger diesel 100 kW, ordinary transmission 0 kW

Using a standard transmission, the smaller diesel will have significantly lower acceleration needed to deal with traffic. As such, it will slow down going up grades and otherwise be seen as a traffic barrier like a small, commercial utility vehicle. But it will have lower engine overhead from internal friction needed to keep the engine spinning and the slower, overall speeds will reduce rolling and aerodynamic drag. The brakes will convert kinetic energy into wasted heat every time they are used.

The larger diesel with standard transmission will accelerate faster and maintain speed going up and down ordinary hills and mountains. However, the engine overhead fuel consumption will be higher. This is the fuel needed to keep larger pistons, valves, engine oil pump and water pump functioning. The brakes will convert kinetic energy into wasted heat every time they are used as is common in urban traffic.

The smaller diesel with a hybrid transmission will have the power to perform like the larger diesel with some limitations. It will run out of steam going up significantly large mountains but hills in range of 100-200 m. will not be a problem. The lower overhead of the smaller engine will reduce fuel consumption at all speeds and the ability to recover a significant portion of the kinetic energy when braking minimizes waste heat. Best of all, the smaller engine can be cycled OFF when running at low speeds and cycled ON to generate power to maintain speed and store the energy needed for the next engine OFF cycle.

When the smaller diesel is in power generation mode, the somewhat fixed energy loss of engine overhead is a smaller percentage of the power generated to sustain speed and charge for the next engine OFF cycle. For example:

• 65 km/h (40 mph) -> 6 kW (8 hp) for an NHW11 sized, compact sedan
• small diesel: 6.5 kW - 0.5 kW (overhead) -> 6 kW needed :: 6 / 6.5 ~= 92% net efficiency
• small diesel + hybrid: 12.5 kW - 0.5 kW (overhead) -> 50% to wheels, 50% to hybrid storage :: 12 / 12.5 ~= 96% net efficiency

Now I've omitted a lot of details to emphasize the engine efficiency gain because its internal friction load remains relatively fixed relative to power generated. If we factor in the thermal dynamic efficiency, that 4% difference triples to nearly 12%, a significant performance improvement. But even this 4% difference increases at slower, urban speeds when the energy demands are much, much lower.

Now I've assumed the same diesel cycle in all cases. If we run the same analysis and include the efficiency gains of an Atkinson versus Otto cycle, the differences in the gas-powered world are even more substantial due Otto cycle, partial power, throttle plate losses.

This is a simple model built to emphasize how engine overhead becomes a relatively smaller part of the net power demand. No fancy cycle changes are needed to demonstrate the hybrid advantage.

Bob Wilson

[Arragonis]

Originally Posted by bwilson4web

I'll try to give an answer with these assumptions whose ratios somewhat match the parameters of the 1.5L/1.8L Prius:

I agree on most of this in terms of maths etc. However the real world kind of knocks that all out. The US market is not the world market, neither is Europe but most Diesel cars are sold here.

In Europe the majority of Diesel cars are SMALLER than a Prius - e.g. Yaris sized. Toyota even make a Diesel Yaris for sale here, its actually quite good - chain cam, common rail, direct injection. Take one of those, add the weight and motors for Hybrid-isation and you kind of hit the point where the gain is less than just leaving the small Diesel alone.

Even Toyota struggle - they sell a Diesel Auris (Corolla sized) here with mega MPG (50+ imp) and also try and sell a full Hybrid (petrol) one as well. Not surprisingly nobody wants the Hybrid. Too spendy. The Prius is not sold here as a fuel saver, more as a posing vehicle for wealthy greens.

But then again, lets go bigger. Take the Peugeot 407. Its about the same size as a Chevvy Impala - more or less. It has the option of a 1.6 HDi Diesel engine - 110hp and 150+ lb.ft of torque. Whenever I drive down a UK motorway and wander out into the overtaking lane, some muppet in one is pushing me out of the way, it doesn't hold up traffic in any way at all.

Ford sell the Transit connect you get in the States even with a 75hp Diesel, amongst others. Again, its not slow enough to hold people up, even fully laden.

On top of this of course is the fact that most European cars are manuals. Hybridisation (Toyota style) works best in Autos or CVT.

So why would I choose to buy a Hybrid Diesel vs a non-Hybrid one ?

Take the history of Diesel power vs MPG
1989 - 92 bhp, 48 mpg (Peugeot 306DT)
1991 - 90 bhp 50 mpg (VW TDI)
1991 - 105 bhp 50 mpg (Rover 220 SDi)
1995 - 110 bhp 50 mpg (VW TDI)
2000 - 130 bhp 50 mpg (VW TDI)
2002 - 90 bhp 60 mpg (Peugeot HDi 1.4)
2003 - 150 bhp, 45 mpg (VW TDI)
2004 - 110 bhp 60 mpg (Peugeot HDi 1.6)
2005 - 150 bhp 55 mpg (GM Europe CDTI)
2006 - 90 bhp 60 mpg (FIAT / GM Europe CDTI)
2003 - 75 bhp, 65 mpg (VW TDI Bluemotion)

So why with the potential for a 1.2 3 cyl TDI giving maybe 90-100hp and 0-60 in 10-11 secs and a top wack of 100-110 and with 60-65 mpg in a typical European car would I want to bother with a hybrid ?

Especially as an Ecomodder I could maybe add 10 MPG to that figure without trying hard ?

[Arragonis]

Originally Posted by Billy_BAD_Boy

@Arragonis only time will tell! But I am sure for the success of diesel hybrids ... at least in Europe

I will sit and wait to be convinced, whilst also watching for the 1.2-1.4 Diesel hatchback with a 100 mpg potential.

I think that will come first, and it won't be a hybrid.

[Billy_BAD_Boy]

100 mpg but in super mini class.

Lets look at that. Peugeot 3008 hybrid

74.4 imp.mpg (3.8/100 ) combined.
ZEV mode
4X4
1600+ kg.
200 hp combined
500 Nm max (in overboost mode)

Not bad at all ...ah

If we compare with the non hybrid 2.0HDi 163 hp version":

Combined cons. 42.2 imp.mpg (6.7/100)
163 hp 340 Nm torque
emissons 176 g/km vs. 99 g/km for the hybrid

The only minus I would think of is the price. Probably 10 to 15% above the non hybrid.

[bwilson4web]

Originally Posted by Arragonis

. . .
So why would I choose to buy a Hybrid Diesel vs a non-Hybrid one ?
. . .

I'm a great believer in the right tool for the right job and the wide selection of vehicles and local requirements means there is an optimum solution for each case:

• less than 12,000 km (7,500 miles) per year - it doesn't matter as long as it can handle the largest number of passengers, luggage and any towing requirements.
• 12,000 -24,000 km (7,500 to 15,000 miles) per year - it dependes upon the mix of urban, extra-urban trips and their relative frequency along with relative fuel costs.
• over 24,000 km (15,000 miles) per year - it depends upon the mix of urban and extra-urban travel.

Factors leaning towards a hybrid:

• mostly urban travel - where slower speeds, the engine ON/OFF cycling and regenerative braking improve vehicle efficiency

Factors for diesel (or gas)

• mostly long distance, extra-urban, travel above 110 km/hr

Factors leaning toward an electric:

• exclusive urban travel of daily distances under 40 km.

Factors leaning towards gas:

• frequent, rapid accelerations needed and no concern for fuel costs (aka., the Top Gear solution.)

Understand the original question had to do with why a diesel hybrid versus a smaller or larger diesel. But when the scope expands to why any one individual should go with one vehicle versus another, we have to go back to requirements and let them drive the optimum solution. Sad to say, there are many often obscure and non-financial requirements and these have to be weighted too. This is a much more complex problem.

One side comment, there is no single mileage number for any vehicle that accurately predicts 'in service' performance. For example, this is my constant speed, MPG vs MPH (fuel consumption versus speed) chart:


But in reality, this is the distribution of mileage in service:

It varies by temperature and activities so I don't get too worried about individual tanks. I'm reasonably happy with my current 52 MPG and am working on the next step.

Several years ago, some Jetta TDI diesel advocates came to a hybrid site claiming the Prius mileage was rubbish and we should all go get diesels. But it turns out there is a USA government web site where individual owners can record their mileage and collecting the data, we found these user mileage values:

Notice there are some areas of overlap. There may be individual cases where someone would get better mileage with a Jetta TDI than an NHW20 Prius. It has to do with the specific driving profiles. What I'm suggesting is we can craft any set of requirements to dictate the answer. The better answer is to look at the requirements and let them dictate the best answer.

Bob Wilson

ps. We had one diesel advocate claim the Jetta TDI was getting a falsely low "official" mileage number. So I looked at the data and sure enough, they were right:

However, the differences relative to the "official mileage" did not make up for the relative, in-service performance. The Jetta is a compact car compared to the Prius, full-size, hatchback.

[Arragonis]

Bob,

Thats a lot of stats

I will concede that should I be the kind of driver who spent most of my time driving only in town then actually a Hybrid may make some sense - even if only for the convenience of self-shifting to deal with stop-start.

Not sure about the Jetta = Compact Car vs Prius full size argument. Looking at the parked side by side and the interior space they seem very similar. And of course with a Jetta you get the option of an estate / wagon. The Prius is better than a lot of other Hybrids in losing little interior space as it was designed to take the battery packs. A conventional car tends not to be - so you get compromises like the battery pack in the Focus Electric taking up the whole boot - I know a hybrid battery would be smaller, but I'm tapping general ideas.

A couple of questions if I may. Do you know how the Atkinson engine compares to the Diesel in terms of efficiency ? Nobody as far as I know is following Toyota down that lonely path. And secondly is the 3rd Gen Prius an Atkinson unit ?

[bwilson4web]

Originally Posted by Arragonis

. . .
Not sure about the Jetta = Compact Car vs Prius full size argument. . . .

It has to do with how the USA measures and classifies different cars based upon body volume:

• Prius, NHW11 sedan body (2001-03), compact car
• Jetta TDI, compact car
• Prius, NHW20 (2004-09), full size car
• Prius, ZVW30 (2010-current), full size car
• Jetta Sports Wagon TDI, station wagon

http://www.fueleconomy.gov/

Originally Posted by Arragonis

. . .
A couple of questions if I may. Do you know how the Atkinson engine compares to the Diesel in terms of efficiency ? Nobody as far as I know is following Toyota down that lonely path. And secondly is the 3rd Gen Prius an Atkinson unit ?

Ford and Toyota use the Atkinson cycle in their hybrids. From the Toyota SAE papers, the 1.8L brake specific fuel consumption overlaps earlier diesel engines but this can be misleading without the 'operational line.' The operational line is the rpm-torque curve the engine follows through the graph of the brake specific fuel consumption:


One of the little understood aspects of the Ford and Toyota hybrid transmissions is the role of the 'generator' (aka., MG1.) It has two modes that either takes or feeds a fixed percentage of the power from or to the engine, 28% (more about this later.) Since we can easily measure MG1 torque and speed to calculate the power, we can divide it by 0.28 to get the operating engine power. Then we can calculate the fuel consumption using either injector timing and rpm or the mass air flow data. I've used this technique to plot relative, fuel consumption from various trips:



This plot shows real world measurement of our 1.5L Prius along the operational line:


These charts give a clue as to the peak efficiency range of the engine based upon rpm. Efficient driving means staying within the sweet range and avoiding, if possible, rpm ranges that are less efficient:

• 1,300-2,600 rpm - efficient
• 2,600-3,200 - power and less efficient
• 3,200-4,000 - required when climbing hills
• above 4,000 - let's burn a lot of gas!

I mentioned power flows either to or from the engine side of the power split device at a fixed rate by the generator, MG1. In both modes, the generator is providing counter torque. At low speed, the power flows from MG1 around the power split device and merges in the big motor, MG2 to power the wheels. At higher speeds, power flows from MG2 back to MG1 which provides counter torque to keep the engine running at a lower, more efficient rpm. It took me a long time to understand this flow but this earliest plot shows these two modes:


One last data point, these metrics explain how my vehicle mileage improved as I learned how to keep the vehicle maintained for efficiency and efficient operational modes:

But this just illustrates our human ability to learn and maximize results. The far left points came from when I bought the car and drove it 1,300 km back home. It was in the Fall and the first dip came from cold weather operation and lessons learned about tire pressure and transmission lubrication. So now, I just drive it and get a solid 4.52 l/100km (52 MPG) over a combination of urban and extra-urban driving. This is our NHW11 model, 1.5L, sedan style Prius.

Bob Wilson

[Billy_BAD_Boy]

Bob ... do you plan buying a diesel hybrid?

Really appreciated your last two posts.

However I still believe that diesel hybrid will have some advantages over gas hybrids.

I am closly monitoring this Peugeot 3008 ... I have no patience to test drive it.

[bwilson4web]

Originally Posted by Billy_BAD_Boy

Bob ... do you plan buying a diesel hybrid?

Probably not since I have a 2003 Prius I use for commuting and we bought a new, 1.8L Prius in May 2009 for my wife. We're pretty well set as far as Prius are concerned.

I'm 61 years old which means our 1.8L Prius will be paid off and in good shape when I have to take retirement.

Originally Posted by Billy_BAD_Boy

. . .
However I still believe that diesel hybrid will have some advantages over gas hybrids.
. . .

The nice thing is Ecomodder is the place to 'build your own' and demonstrate that it works. This place is awesome when you find someone posting with 'dirty fingernails.' <GRINS> . . . and a few of us still have an old slide ruler.

Bob Wilson