Vehicle Energy Requirement

Why not just convert horsepower to kw?

If I knew the horsepower, it would be easy, but a 300 horsepower 8000 lb. truck with a frontal area of 16 square feet going 70 MPH does not use 300 HP. I need some way of calculating the actual power used. Thanks!

Well, I'll put it here in a very simple form. Then you can go on, research some books and refine your model as you want (or are required to).

Have you heard about Cx? This is an adimensional parameter that expresses the resistance of the air that the vehicle suffers by the frontal area.

Basically, the formula is:

Fa = 1/2 x Ro x S x Cx x V^2

Where:

Fa = Force [N]

Ro = air density [kg/m^3]

Cx = Shape coefficient [none]

V = speed [m/s]

You'll need this parameter from the truck manufacturer, or, maybe, make a model in a wind tunnel (use adimensional parameters to make a scale model, of course) and evaluate it. The formula can be used in the two ways, to determine the force, or the Cx. So, you can calculate the force required to keep your vehicle going on.

At this point, you have the force, and the speed. You may know that, if you multiply the displacement and the component of the force in the displacement direction, you obtain what we call work. Divide work by the time, and you have power. So, if you multiply the force required to keep the vehicle going on and its speed, you find the power spent. Of course, use consistent units, I always prefer to use SI everywhere to avoid mistakes.

Of course, dont forget to consider the tires rolling resistance, and the efficiency of the gearbox and differential.

If you're after the real life figures I'd work from the actual vehicle. If you can relate spot fuel consumption back to hp supplied, perhaps by the use of a dyno, you're half way there.

I see a lot of BS so here goes some BSME.

Efficiently Use the properly designed tool for the anticipated work related job.

Do you desire speed, acceleration, jerk, work, change in elevation, large capacity, durability of materials, repeatability of function, moving heavy loads quickly, moving light loads slowly, or do you have anything concrete in mind atol?

To move an object from point A to point B with no change in elevation and no resistance takes the same energy to decelerate (brake) as to accelerate with no total change in energy except for losses dew two efficiency.

Some heavy vehicles in the 1940 & 1950's had only 10 hp IC engines. The metal bodies were thick 10 gauge steel with large narrow wheels to negotiate deeply grooved mud paths. 10 mpg was great mileage on those dirt & gravel roads for vehicles light and large of the day.

Many gears starting with a slow low were used to gain speed from zero or negotiate steep inclines fully loaded. Acceleration (deceleration) manuevers vehicles well in heavy traffic but theoratically is not necessary to move from point a to point b.

The false perception is that large hp translates to low mpg. Not true. The 400 hp vette gets over 30 mpg routinely in real life whereas the small Ill conceived raved about electric vehicles EPA falsely rated for over 50 mpg reportedly rarely in real life can hardly get 25 mpg with strong wind blowing direction of elevation declining travel.

Electric and electric hybrid vehicles powered by grid electricity generated by dirty ole fossil power plants add 40-100 tons pollution annually per vehicle consuming excessive amounts of dino petro, coal, or worse. Obviously huge amounts of fuel energy are wasted to generate 100 tons CO2. Contrary to popular perception, CO2 Pollution is waste energy.

Efficient conversion of fuel to energy is always clean and non-pollutant. Public and private profiteering energy providers obviously disagree. Unfortunately, ignorant populace tolerates the monitarily affordable. To equate the amount of energy required to form one small container of CO2, please visit the local drag strip and observe first hand the extreme burst of energy displayed by a dragster with CO2 boost. That dragster did not create energy. Energy plus inefficiency is equal for the from/to CO2 conversion unless you falsely believe energy is created by the converstion.

The 400 hp vette engine emits less pollution per smile than the small low HP EHV EPA rated for 50+ mpg emits.

If you desire to construct an efficient energy machine, scrutnize the chevy corvette closely. Duplicate the engine conversion process with revisons required for the fuel of combustion. Please do not duplicate the hybrid electric. Grid losses alone in addition to less than 50% power plant efficiency coupled with 30 (west coast) -100 (east coast) tons pollution annually should make any citizen totally cynical of the US EPA and the posted regulated displayed auto mileage ratings.

Perhaps he could run his car on corn.

Hi Cornstoves, I have to disagree with you on a couple of points:

Efficient conversion of fuel to energy is always clean and non-pollutant.

While the efficient combustion of fuels will minimize pollution they all produce pollutants, even hydrogen. First of all with all the fuels except hydrogen there is the CO2 and while there is dispute over how much damage this is doing to the environment it is still a pollutant. Then you have nitrogen compounds that are formed due to the high temperatures of combustion which are really bad pollutants and one of the major driving factors in photochemical smog. There are also an enormous number of other trace compounds, some of which are carcinogenic, that are also byproducts of the combustion of hydrocarbons.

We can do a lot better than we currently are and using renewable fuel sources like inedible corn is a good idea and the products of combustion are generally not that dangerous to the environment but it is not pollution free.

observe first hand the extreme burst of energy displayed by a dragster with CO2 boost

Now I must admit that drag racing is not something I follow but I had a look on the net and could not find anything about CO₂ boosting. I have never herd of this and have no idea how you could use CO₂ to boost the power output of the engine. The only thing I can think of is that you are confusing nitrous oxide with carbon dioxide. If this isn't the case can you please explain how you use CO₂ to get this burst of power.

"The 400 hp vette engine emits less pollution per smile than the small low HP EHV EPA rated for 50+ mpg emits."

I looked up the data concerning the "tons per year" of green house gasses produced for the Toyota Prius, and the Corvette. This is for driving 15000 miles per year, and 55% city 45% highway driving. The vette produces 8.6 tons per year whilst the Prius produces only 3.4 tons per year. The EPA air pollution score for the vette is 3, and the Prius is 9 or 9.5 (out of 10). That number basically says how clean the pollutants are, not how much it puts out. A higher number just means it's cleaner. So the Prius is cleaner... can we agree?

Here's the link:

http://www.fueleconomy.gov/feg/bymodel/bymakemodelNF.shtml

What I don't understand is why all diesel vehicles have a 0 or 1 air pollution score. They do create more pollutants of some types, but use less fuel to begin with, so the overall pollution is less (in my book). My jetta diesel has a score of 0, but I get 50 mpg, and produce only a little more green house gasses per year than the prius is rated for. I don't think their score is right for diesels.

Part of the answer to your question about fueleconomy.gov's scoring of diesel, there are 2 primary issues, from what I understand, NO_X and particulates. Did you notice that only VW has a score, the rest of the diesels are "not available" ... even for 2006 or earlier.

I suspect part of this is partially related to the ULTRA LOW SULFER DIESEL availability ... but for 2007 I have no idea other than NO_X and particulates.

First, let me direct you to my web site. Http://www.mayfco.com When you get that first page, click on the only viable and active link. That will take you to may automotive web page. I do some aerodynamics for the Bonneville salt race crowd and so in the analyses section you will find curves for all sorts of cars and the hp it takes to move them at various speeds. When considering how much power is required, there is not just aero forces at work but a significant rolling resistance as well. One good text I use is by Tom Gillespie and Is "Fundamentals of Vehicle Dynamics": it is an SAE text, and it includes all sorts of information regarding a project like yours. As to KW, remember 746 watts per horsepower. And the text also includes going up and dowh hills and the power requirements for acceleration as well. If you wish, contact me off list and I'll try and help some more. Good luck,

drmayf

Great and interesting work! Thank you. DickL

If you would like any help with your aerospace site, let me know. I have some experience and some knowledge I'd be glad to share.

A couple of thoughts and comparisons:

It appears that hybrid vehicles like the PRIUS and CIVIC require something in the range of 350 to 450 watt-hours per mile (relatively level terrain).

I was trying to compare Btu/mile on several automotive technologies.

Vehicle ===== engine =====mass == Average ==== Btu/mile
-----------------------------(tons)---- mpg
Malibu -----6cyl, 3.5L, A4 ---- 1.59 ------ 25 -----------4720 (gasoline)
Corsa, MY07 1.3CDTi (75PS) -- 1.35 ------51.2 --------- 2541 (diesel)
CIVIC ------1.4 IMA ES -------1.44 ------ 50 -----------2360
PRIUS -----1.5 VVT-i Hybrid -- 1.93 ------ 55 -----------2145
Plug-in Electric (PRIUS like) ----1.93 -------------------- 1339
Whr/mile estimated Energy Consumption ~ 400 Whr/mile
@ 80% charge/discharge efficiency (on board) ----------- 1674
Energy Required: 3X at generator (assume central) ------- 5022

MY Conclusions:
1) Plug-In Electric vehicle can be expected to generate as much or more emissions than the referenced Malibu when traditional fossil fuel generation is used.

2) Hydrogen technology suffers from the same deficiencies as the plug-in without major technology breakthroughs.

3) The only obvious advantage of Plug-In/Hydrogen is it moves emissions from point of use to point of generation.

4) It still seems to "boil down" to more miles per unit of energy for the "mission", i.e., resource conservation.

A great try, but generation efficiency is I believe nearer 60% than 33%, which halves the CO2 for the plug in and proves it is best option. When you factor in that plug-ins are used mainly for city driving, the advantage probably multiplies 2 or 3 fold, This case just shows the lack of real science in todays debates.

If electric generation and delivery (distribution) from fossil is 60% efficient ... that is far better than I assumed.

Does anyone have a more accurate "delivered efficiency" number for the USA?

As I said, the advantage of plug-in is moving emissions away from point of use!

Looking at DOE data, I came up with 10,297 BTU's of coal to deliver 1 kWH (3412 BTUs) at the customer's meter. That works out to 33.1% efficiency. That includes all the losses of production, line losses, meeting EPA requirements etc.

What sort of vehicle? Bicycle? Car? Train? Aeroplane?

Kempe's Engineer's Year Book may prove valuable further reading.

The original question revolved around the efficiency of fossil fueled electric generation and distribution.

...and omitted the mode of transport it was to be applied to.

...and omitted the mode of transport it was to be applied to.

Yes ... just the typical efficiency from fossil fuel (on site) through electric generation and delivery (say 100 to 300 miles) in the USA.

Some say the efficiency is 60% while others believe 30%.

I need a more accurate value.

Can any one provide a better value?

Better values:

Coal: 45%

Natural Gas: 55%

Oil: 38% (probably not many of these)

from the site: http://www.e8.org/index.jsp?numPage=138

Transmission line and distribution losses: 7.2%

http://en.wikipedia.org/wiki/Electric_power_transmission#Grid_exit

So really it was something in between both of your arguments

-Nick

The basis of the comparison needs to be tied down. In a comparison of kWh expended per ton-mile across a range of vehicle types, the bicycle is at the top of the list.

PWSlack: The basis of the comparison needs to be tied down. In a comparison of kWh expended per ton-mile across a range of vehicle types, the bicycle is at the top of the list.

Bicycle is second choice ... I want one of the new 1.3 to 1.5 liter turbo diesels ... but this is the USA. I do not want a VW or Benz. So, for now I'm driving a 95 Honda Civic CX that I plan to convert to a VX ... hopefully that will give me a jump from 40 to about 50 mpg averge.

Maybe Honda/Toyota will deliver vehicles with small diesels by 2009.

I don't even have to do any calculations to say that using electricity would be more efficient and pollute less than having my car powered by an engine. I think of it like this: If it was more efficient, then wouldn't I want to power my house with my car? Most certainly not! I bet you that even with the 7% extra losses from transmission, a multi million dollar power generation plant would be much more efficient than my cars engine that cost maybe a few thousand dollars. It's easier to make something huge more efficient than something small. Huge diesel engines in ships are incredibly efficient (sometimes around 50%) while small diesel engines in cars and trucks are only around 35-40% efficient. It's silly to think that even a coal power plant would be less efficient than a car engine or else we would be running IC car engines on coal dust to power generators! (note: I don't know if it's possible to make an IC engine run on coal dust, I'm just using it to make a point. I'm sure it's possible, coal dust is of course explosive in the right concentrations.)

I would spend some more time trying to find better numbers, but I have lots of work to do... sorry.

Here is the comparison that I develop just to see the relationships for the following.

Gasoline
Malibu (6cyl, 3.5L, A4) @ 25 mpg combined average results in 4720 Btu/mile
Pontiac G6 (4cyl, 2.4L,A4) @ 27 mpg combined average results in 4370 Btu/mile

Diesel
Opel Corsa, MY07 (1.3CDTi (75PS)) @ 51.2 mpg average results in 2541 Btu/mile
Toyota Auris (1.4 D-4D Multi 5) @ 25 mpg combined average yields 2506 Btu/mile

Hybrid
CIVIC (1.4 IMA ES) @ 55 mpg combined average results in 2360 Btu/mile
Prius (1.5 VVT-i Hybrid) @ 50 mpg combined average results in 2145 Btu/mile

Plug-In
Prius like all electric assume 400 watts/mile average yields 1339 Btu/mile
like above @ 80% charge/discharge efficiency yields 1674 Btu/mile
@ 7% line loss+average 45% gen loss=48% efficiency yields 3488 Btu/mile

Conclusions:
1) Plug-In Electric vehicle can be expected to generate about 50% more emissions than the CIVIC hybrid and more than either of the diesels sampled.

2) Hydrogen technology suffers from the same deficiencies as the plug-in without major technology breakthroughs.

3) The only obvious advantage of Plug-In/Hydrogen is it moves emissions from point of use to point of generation.

4) It still seems to "boil down" to more miles per unit of energy for the "mission", i.e., resource conservation.

I'm just trying to sort it all out.

Any thoughts?

I think the whole point of this debate (actually I think it's a hijacked thread?) is that you have to do the calculations. I don't know one way or the other but I do know that every step of the way from the coal pit to the torque in your rear axle there's losses and inefficiencies whereas the petrol car, once the fuel is in the tank, has very few.

If it's any help I've recently been doing some work at a natural gas power station. Their gas turbines work at about 19% - 20 % efficiency. That's fact, I've watched the metered gas consumption v power output and done the sums. If you don't mind waiting until my next visit I can post the figures for others to check. Just don't ask where they come from that's all!

I believe a gas/steam/turbine plant with heat recycling is more like 40%.

These big plants fair chuck the energy in. If you could buy the equivalent bangs worth of petrol for the prices they pay you probably would run your house off a little gen set.

Hi Nutwood, I found your comment about the efficiency of the gas turbines you are using interesting.

If it's any help I've recently been doing some work at a natural gas power station. Their gas turbines work at about 19% - 20 % efficiency. That's fact, I've watched the metered gas consumption v power output and done the sums. If you don't mind waiting until my next visit I can post the figures for others to check. Just don't ask where they come from that's all!

I believe a gas/steam/turbine plant with heat recycling is more like 40%.

I must admit I thought they were somewhat more efficient than that but none the less I was not too surprised. I did however have a look on the internet and found the GE H System^TM which is one of the combined gas steam systems that you referred to but they are claiming to have broken the 60% barrier.

Regardless of them breaking it even getting over 50% wipes the floor efficiency wise over most fossil fueled power plants.

Let me get this straight masu, nutwood, and everyone else:

efficient gas fired turbines are somewhere between 40 and 60% efficient ... so considering running inventory age and condition 50% efficiency is probably a fair estimate. Distribution losses can be estimated at about 7.5%.

This results in an overall efficiency of 43% in to out. If this is then applied to a plug-in electric vehicle with an 80% (I'm not sure of this value but it should be in the general range) charge/discharge efficiency, then the efficiency should be about 33% to the drive motors.

This then suggest that 0.4 Kwhr/mile {estimated from the Prius} reflects back to the generator as 1.2 Kwhr/mile (or about 4 KBtu/mile).

Is this generally correct?

If this is correct then the plug-in electric vehicle consumes about the same energy/mile as the Pontiac G6 2.4L 4cycl, A4 (rated 27 mpg(US) average) which consumes about 4.2 KBtu/mile.

Any noticeable errors in logic or math?

From what I can see of your calculations it seems to confirm what I have suspected in that using electricity from the mains to power vehicles is not the answer most people think. I havn't looked at your figures in detail though as they are in imperial units which are meaningless to me so I need to convert them to something I understand.

With the increasing price of petrol of late I did some calculations a while back to see if electricity was cheaper than petrol on a purely energy basis. The break even point in Sydney Australia was around AU$1.16 a liter but this however doesn't take into account the efficiency of engines and regenerative breaking. If you take these into account the break even point is about AU$0.75 a liter on normal power and about AU$0.30 a liter with discounted off peak power.

As I said though these figures are only on a cost basis and not overall efficiency. If I get a chance I will go over the figures for vehicles in Australia and see how they compare but at the moment I still have 10 threads left over from yesterday that I havn't managed to get to yet.

What we need to be doing is stuff like this: this:http://www.treehugger.com/files/2007/02/the-opel-eco-speedster.php

Sure, that's a race car, and isn't practical for most people, but why aren't there passenger vehicles that get 113 mpg here? It even says that GM (the parent company) isn't interested in bringing that vehicle into the US, or any fuel efficient vehicle here for that matter.

Back to the original post, power requirements to go 155 mph... 1.3-liter ECOTECH CDTI diesel engine. I wouldn't mind having one of those...

How about the Tesla Motors Roadster, it can do 0-100 K/Hr in slightly over 4 seconds.

masu: How about the Tesla Motors Roadster, it can do 0-100 K/Hr in slightly over 4 seconds.

I'll bet that is "a bunch" of KW hours! I understand that at one of their demos of a high G take off, they have to push it back to the start point.

Acceleration can be costly. I estimated that about 1/2 to 2/3 (possibly more) of the cost of fuel goes into being able to achieve 0 to 60 mph in under 8 seconds for any IC powered vehicle with that capability.

Acceleration can be costly. I estimated that about 1/2 to 2/3 (possibly more) of the cost of fuel goes into being able to achieve 0 to 60 mph in under 8 seconds

I don't find that the slightest bit surprising, however with an electric car you can get a not unreasonable portion of this back with the use of regenerative breaking. City driving, where you spend a considerable portion of any trip accelerating and decelerating, is where electric vehicles really start to outperform their standard fossil fueled counterparts. The more sporadic the trip the larger the gap between the overall efficiencies becomes.

Whilst electric cars can't and will never be able to recover all the energy during deceleration the proportion they can recover is increasing. As the performance and capacity of super capacitors increases I think we will see, in the not too distant future, far more efficient regenerative breaking systems.

As our roads become more congested the problem is only going to worsen. However as breaking systems become more advanced with more of the energy becoming recoverable conventional vehicles are going to find it increasingly difficult to remain competitive.

Medium size gas turbine engines (aircraft engines modified for power generation) that one might find at a co-generation facility have mechanical efficiencies of about 20%. The hot exhaust has a high O2 content and is then normally directed as combustion air to a boiler to produce steam for heating or power generation. This would be for engines in the hundreds of kilowatts to low megawatts.

The figures you are quoting are what I have observed in real life situations. Quoted efficiencies are all very well. But nothing beats standing there and seeing the metered fuel going in and the metered power coming out. My 19 - 20% figures came from a bunch of 35Mw units and they were all the same, give or take a bit. There was no co-generation so the waste products were just that.

There's a lot of well engineered new stuff that's pushing up around the 60% but if you're quoting figures in an electric car debate you really have to use the figures for what's actually out there now and I can assure you a lot of it's pretty poor.

I'd be happy to give you the figures at several speeds and several grades -- I have a spreadsheet set up for just that purpose. Your frontal area cannot be correct for a truck (16 sq ft is too small). If you don't have the actual CD value for the vehicle, tell me what it looks like, and I'll estimate.

I'd need:

Weight

CD

Frontal area

This is a sideways answer (skipping speed, frontal area, and weight).

The GM "VOLT" is reported to consume 400 W-hr/mile from a 16 KW-hr 400 pound battery pack resulting in a 40 mile range on battery. The 400 W-hr/mile is consistent with my Prius estimate. These values are based on driving cycles that are unknown to me, but educated guess is the "new 2008" EPA cycle.

http://www.ecoworld.com/blog/2007/03/16/the-e-flex-auto-revolution/

Concern: what does a 50 W sound system or laptop computer do to battery range?

Of course there is an onboard IC engine (50 mpg is reported) to supplement the battery as needed, so my question is only relevant to battery ONLY applications ... 40 a mile range may be adequate for most users. The consumer would need sufficient information to make the judgement for him/her self regarding "all electric mode" range if the vehicle ever comes to market.

I think your 400 W-hr/mile estimate is probably valid. Hymotion, who makes a plug-in kit for the Prius claims 50 km (30 miles) from a 5kW-hr LI battery. (The standard Prius battery is 1.5kW-hr.) Their claim seems very optimistic (166W-hr / mile).

Certainly, AirCon loads adversely affect range, with Prius mileage dropping 25% or so when the AC is running hard. A 50 W stereo rarely actually produces (or consumes) 50 W, so its effect, and the effect of most electronics, would be fairly slight. Headlights are typically 50 watts each -- significant, but not crippling. Even if all the accessory loads were a full kilowatt, that would only use up 1/16 of the Volt's battery charge in one hour (and the propulsion system would have used up the rest in moving you 37.5 miles in that same hour.) (Of course a 16kW-hr battery does not deliver 16 kW for an hour, but for discussion purposes, it's close enough: a Prius doesn't require 16kW to make it go 37.5 mph, after all.)

Interestingly, these LI batteries are hideously expensive. The 5kw-hr kits are about $10,000, and weigh 170 lbs. Lead acid would weigh 280 lbs and cost $500.

This is a complete aside but you may find it interesting. I have an astronomical telescope tat has a microprocessor controlled mount for finding and tracking celestial objects. It can be powered internally from 8 AA alkaline batteries or externally from a 12V supply. Currently I am using a 7.5 Ah sealed lead acid battery to power it.

It chews batteries at an incredible rate, but even if I used the SLA battery only once it would be cheaper than using the AA alkaline batteries.

SLA batteries are always worth considering and it can often be hard to do it cheaper.

You must be "plumb crazy" to use an SLA.

(The term "Plumb crazy" of course, came about from the mental degeneration that lead workers -- plumbers -- endured.)

Yes SLA batteries are comparatively easy to recycle (despite the nasty metal) and given some good engineering and a little rearrangement of priorities can substitute very well for the more fashionable batteries.

I too have a telescope with a microprocessor in it. Mine, unfortunately, does not do the tracking -- it just tells me how to manually move the thing to find an object, once I have set it up and leveled it. Nevertheless, it's pretty easy to find stuff that otherwise would be hard to locate. I should get it out again soon -- good thing to do with the kids.

"The 5kw-hr kits are about $10,000, and weigh 170 lbs. Lead acid would weigh 280 lbs and cost $500."

Where did you find 5kWh lead acid battery kits? The best I could find were 3.1 kWh batteries that cost $750, and weighed 160 lbs. If equivalent power lead acid batteries cost 1/20th of the LI batteries, and still only weigh about 110 lbs more it seems silly to use LI. Adding an extra 110 lbs wouldn't be any different than carrying a fat passenger instead of a thin one. hahaha. That 3.1kWh battery was only 1.34 cubic feet, I think the energy density would be very comparable to LI.

When lead acids are treated properly they can last a long time (probably longer than LI). The original battery in our 1998 F250 still has something like 500 cold cranking amps available.

Nick

There is not a prepackaged SLA kit for a Prius. To come up with 280#, I calculated the weight of 5kW worth of deep cycle (marine) batteries. Typically a 65 AH battery is 40 lb. 65 x 13.2 = 858 WH 5000/858 x 40 = 233 lb (about 6 batteries). Generally a 65 AH battery will cost about $75, which times 6 would be $450. I then added a couple fudge factors to cost and weight.

This is not a completely fair comparison to the Hymotion Prius battery, because it is higher voltage, meaning more (smaller AH) batteries would be required. The smaller units would cost slightly more per AH.