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395 messages, Last post on Aug 29, 2007 at 7:27 AM
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Replying to: marcb (Jun 08, 2006 5:42 am) Very impressive, but still slightly over-expensive. Hybrid cars have an advanage in transient driving conditions (accelerating, decelerating) in that they can recover energy via regenerative braking, and re-use it for acceleration. The current gasoline-hybrids are not very successful in Europe because the hybrid gives minimal improvement (and perhaps even some disadvantage due to weight) in highway / motorway driving - in these conditions a gasoline-electric hybrid cannot match a good diesel. For example, a euro-spec Prius uses 4.2 l/100km on the EC extra-urban cycle, while a similar-size Renault Mégane 1.5dCi 106hp uses only 4.0 l/100km on the same cycle. By combining a hybrid with a diesel engine you get diesel efficency on the motorway, combined with the advantages of regenerative braking and engine shut-off in transient conditions. Bear in mind that its not just stationary idling when the IC engine can be shut of in traffic, but also low speed driving and when slowing / braking / coasting. A diesel may use very little fuel when idling, but it still uses fuel (and creates noise and pollution). The problems with the diesel hybrid beyond that of a petrol hybrid are cost (a turbo-diesel engine already costs more than a petrol engine), packaging (the underbonnet package has to accomodate the turbo installation, a more robust engine block, and the hybrid hardware) and smooth transition between electric only and IC power due to the greater torque required to start a diesel engine combined with its greater torque output at low revs - if you tried to use a system similar to Honda's IMA or Toyota's Synergy Drive, you would have severe driveline shunt to cope with. The PSA/Ricardo/QinetiQ prototype gets round this by using a separate starter/generator to start the engine while decoupled from the electric drive, then speed matching the engine to the drive before coupling it (just like any car with an automated manual transmission) - not as efficient, but much smoother. |
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Replying to: neil733 (Oct 26, 2006 4:19 am) My limited knowledge on diesels is going to be exposed here, but here are the thoughts generated by your post: 1. Seems to me that the "auto-stop" feature on a diesel hybrid would be a problem, but with the VW Lupo diesel that supposedly has an "auto-stop" feature, maybe I'm off base on that. Don't diesel trucks idle a lot because restarting all the time is an issue? 2. As far as the "turbo" on a diesel engine - a diesel/hybrid would eliminate the need for the turbocharger because the hybrid drive with it's added torque and added power would be available for that extra ooomph when needed. I feel like my TCH has a turbo when I floor it and see the gas and electric motors combining to give me that "pushed back in the seat" feeling. All these problems have been overcome in larger diesel/hybrids like the trucks and buses which are all around the world. So why it's so difficult to get it all together for a passenger sedan is a mystery to me. Seems like the company who could (and should) do it the easiest and fastest would be Honda with their IMA system, since they have their own new spanking diesel engine for the Accord diesel, and they already have an Accord gasser hybrid. Seems like blending those two would be about a 6-month project. What's the holdup dudes??  
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Replying to: neil733 (Oct 26, 2006 4:19 am) Thank you for the first hand report. |
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Replying to: larsb (Oct 26, 2006 6:14 am) The biggest problem is cost. As you know many communities would adopt the hybrid buses. They have a tremendous price difference. Last study I read by a municipality the payback was 57.5 years. No bus will last near that long. Average cost of a conventional diesel bus is $300k. Average diesel/hybrid bus is $500k to $600k depending on manufacturer. Advertised fuel economy gain 30%. Actual gain over regular diesel bus is as little as 10%, according to the study done by the Connecticut department of Transportation. |
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Here is that study. Pretty comprehensive. Any city thinking of buying new buses should look at all options. If you have Natural gas it may be a better choice than a diesel/hybrid bus. http://www.ct.gov/dot/LIB/dot/documents/dresearch/CT-170-1884-3-04-5.pdf Who have bought hybrid buses? State by state count. http://www.hybridcenter.org/hybrid-transit-buses.html
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Replying to: larsb (Oct 26, 2006 6:14 am) Well, I don't think it really eliminates the need. You are right, of course, that the electric drive would add to the pickup, but in a diesel, the turbo helps in more ways than just acceleration. Due to the very high compression ratio in a diesel engine, it requires quite a bit of air. More than a gasser. So even at highway speeds, a turbo is helping to get enough air into the cylinders so the engine runs more efficiently. At least, this is my understanding. PLUS, on the power side, why take away that which makes a diesel appealing by today's standards? With a turbo, today's diesels can keep up with the gasser alternatives. Without it, power-hungry folks (myself included) would not want to make the performance sacrifice and pick the diesel alternative. |
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If going to diesel could be done at no cost, fine, but adding a diesel to a hybrid, while certainly improving mileage, likely would not pay. This is the hardest thing to understand - going from, say, 25 mpg to 50 mpg generates much more savings than going from 50 mpg to 75 mpg. Over 100,000 miles, going from 25 mpg (4000 gallons used) to 50 mpg (2000 gallons used) saves 2000 gallons (which means you'd have to drive 50,000 just to pay off the $2800 spent on a hybrid Civic, assuming $2.80/gallon!). Now, assume a diesel hybrid gets 75 mpg. It would use 1333 gallons over 100,000 miles, a savings of only 667 gallons from 50 mpg, one third the savings from the 25 - 50 mpg step. Using the $1400 increment for a diesel Jetta, it would take about 75,000 miles to pay off the cost. If you start with a diesel to get to 50 mpg (25,000 miles to pay that off), then add the hybrid mechanism for $2800 additional to get to 75 mpg, it'll take 150,000 miles to pay that off. Way too long for any mass market. A better question is this - why hybrids at all, if a diesel can get about the same milage improvement for 1/2 the cost? I'm looking forward to Honda's new diesels.
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Replying to: texases (Oct 26, 2006 9:39 am) You are way too practical and logical for this thread 
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Replying to: midnightcowboy (Sep 13, 2006 10:54 am) It's all in what you want to drive. |
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