Klean Diesel Kaput

I'm thinking of a specific thread to compare and contrast the different cycles. Basic thermodynamics, a review of the physics.

Actually I've found that site to be fairly accurate. With rare exception, the members are very much into the scientific method ... doing experiments to test hypothesis. Of course, not universal, it is one of the best collection of credible, experimenters and investigators outside of "Prius Technical Stuff."

I've visited the TDI site from time to time and was able to get the TDI data for this chart:

I very much appreciated getting steady-state, TDI data from "Plus 3 Golfer." But I don't 'hang there' because I don't feel the need to 'witness' or be a hybrid/Prius missionary. It turns out I don't have to go there as so many diesel advocates come to Prius forums, Edmunds and PriusChat. We have plenty of volunter diesel missionaries to work with here. <grins>

Is that a 1997 engine?

I was looking for more recent, 2.0L TDI BSFC, which I found at Ecomodder:

Sad to say, it does not include the automatic transmission operating line. In fact, I wasn't expecting to find it, in contrast to the Prius:

But let's go back to what the "operating area" or "operating line" means and why it is important.

OPERATING LINE OR AREA

A simple inspection of the 1.8L Prius or 2.0L TDI engine shows a series of areas whose edges separate the different specific fuel per unit of power. To claim "my engine has xxx g/k Wh and thus better than your yyy g/k Wh" is nonsense if the engine never or very seldom operates in the area. The delivered efficiency is the percentage of power, the "k Wh" at any given point in the BSFC chart. For example, let's look at what happens on a typical trip of say 88 minutes, identical urban route:

	Column 1	Column 2	Column 3	Column 4	Column 5	Column 6	Column 7
0	BSFC	min. diesel	total	min. Prius	total
1	200	1	200
2	210	2	420
3	220	5	1	100	50	11	000
4	230	10	2	300	20	4	600
5	240	20	4	800	10	2	400
6	250	50	12	500	5	1	250
7	260			2	520
8	270			1	270
9		88	21	320	88	20	040
10		Diesel BSFC	242	Prius BSFC	228

*semi log scale used for duration

In this drive, the Prius achieves a much higher, specific fuel efficiency because it maximizes the time at peak BSFC. It can do this because:

• computer controlled transmission - selects the optimum gear ratio to keep the engine in the "sweet spot."
• engine off in inefficient regions - the Prius is notorious for turning off the engine instead of burning gas at idle or while braking.
• battery charging storage at peak efficiency - the engine generates a little extra power and stores it in the battery. This energy is later used to handle low-power situations so the engine does not have to run.

So this is why the "operating line" or "operating area" is so important to superior Prius mileage. It is why trying to make some claim based upon BSFC chart without the operating line is at best ignorance. So lets compare and contrast "clean diesel" fleet performance versus to Prius performance.

One of the unique features of the Prius is the ability to read out engine torque and rpm. The product and a constant is the engine power. Combine that with the fuel consumption, available from either injector timing or mass air flow, and every Prius has a built-in, dynometer. So I was able to make my own BSFC chart from data collected from my Prius:


Bob Wilson

 

This is why I enjoyed the VW commercial:

VW claims their cars are louder than the Prius, which we agree.

Bob Wilson

 

No problem since Ecomodder's goal is improving vehicle efficiency. It was what initially piqued my curiosity. Then I saw how they approached it and realize the value of that group. Remember, I'm curious, not a missionary.

Great, I look forward to seeing the folks who 'read BSFC' prove the courage of their convictions and bring their own charts. Hopefully, something current.<GRINS>

Not likely as we already have two Prius and an RV.

Bob Wilson

 

This is the same table re-ordered to more clearly show the impact of the operational line or area:

	Column 1	Column 2	Column 3	Column 4	Column 5	Column 6	Column 7
0	BSFC	minutes diesel (*)	total	minutes Prius	total
1	200	1	200
2	210	2	420
3	220	5	1	100	50	11	000
4	230	10	2	300	20	4	600
5	240	20	4	800	10	2	400
6	250	50	12	500	5	1	250
7	260			2	520
8	270			1	270
9		88	21	320	88	20	040
10		Diesel BSFC	242	Prius BSFC	228

* - pure speculation, we need user diesel data.

I understand diesel advocates may have access to torque sensor data. If they can combine that with engine RPM and injector timing, they should be able to make a chart like this:

You'll notice there is a strong clustering of HP data points in the 1,400-1,800 rpm region and then it tapers off at higher power settings. This usage pattern overlaps the region of highest BSFC.

Bob Wilson

 

If the diesel vehicle has a way to report the rpm, torque, and injector timing, just record the data in normal driving. That is what I did.

A proper BSFC chart requires the engine in a dynometer, standard fuel and well controlled conditions that includes no accessories. These overhead functions in a vehicle driving on streets mean I can't replicate the exact values published in the Toyota papers nor will in situ measurements of diesel efficiency report the same values as the lab charts. So I did a two-pass analysis.

I first calculated all specific fuel consumption data including removing outliers, more about this later. I then created buckets based upon the highest, specific fuel efficiency, 100%. I then made categories based upon 5% bands of efficiency. This in turn was used to generate plots using different diameter and colored data points.

Field data suffers from sampling race errors as these are not recorded at exactly the same instant in time:

• rpm
• torque
• injector timing

These can result in 'impossible' values or outliers. To eliminate them, I only use data points where the two values at times T{n} and T{n+1}, vary by no more than 10% for all six data points. It means I don't get transition values but rather a collection of steady-state values. This takes out negative HP and other impossible values.

I would enjoy sharing techniques and data with a diesel enthusiasts bringing empirical data. But I feel uncomfortable discussing it at the TDIclub site because it would look as if a Prius advocate were coming to 'pick a fight.' If they would feel uncomfortable sharing the data in this diesel forum of PriusChat, Ecomodder would be a suitably neutral site.

Bob Wilson

 

Can you appreciate the irony of posting photos of smoking diesels in a sub-forum of PriusChat? There is a concept of 'know thy audience.' Perhaps fuel efficient folks like Prius owners are going to form an impression from:

• Enthused to see diesels generating great clouds of smoking tires and exhausts
• Suddenly interested in diesels that are obviously burning huge amounts of fuel to go short distances
• Entranced at diesel engine and tire noise

Seriously, what were you thinking? Was it something like, "I'll show those Prius folks what they are missing ..."

You've succeeded but don't take it personal. You weren't the first and no doubt won't be the last. It seems to be an attitude VW instills in their advertising and on to their enthusiasts. The most recent being the amusing Superbowl ad:

I enjoy the irony of seeing a German company showing another kind of 'police state.' The clearest message from this ad is 'screw Clean Diesel, we don't need no environmentalism.'

It isn't you but rather whatever passes for marketing in VW/Audi that is sending out the schizophrenic messages. I'm just surprised you haven't appreciated the irony.

Bob Wilson