Category: Transportation

Anything related to transportation, including cars, traffic, other modes of transport, and so on.

Post #1775: Gas versus electric mowing, Part 5: Finally, a sensible estimate

To cut to the chase:  I use a 21″ push mower with a modern Honda overhead-valve engine.  Starting from EPA data on emissions for engines of that type, I calculated two simple rules of thumb, for the pollution generated by my lawn mowing.

If the standard of comparison is the typical car on the road — call it a mid-2010s full-sized sedan — then gas lawn mowers are 100 times dirtier than gas cars, per horsepower.  And an hour of mowing generates about as much pollution as an hour of driving.

That’s just the mower.  That doesn’t include emissions from your gas can, as outlined in the just-prior post.

Also see Post #1776, explaining why, despite this level of pollution, I’m not going to switch to an electric mower any time soon.  This, even though I drive an electric car (Post #1924, et seq.) Continue reading Post #1775: Gas versus electric mowing, Part 5: Finally, a sensible estimate

Post #1774: Gas vs. electric mowing, part 4: A correction on vapor recovery, and why you’re not supposed to top off your car’s gas tank.

 

In my just-prior post, I was about a decade out-of-date in my understanding of the gas vapor recovery systems installed on U.S. gas pumps.  I’m going to correct that here.

  1. Gasoline vapors are a major contributor to photochemical smog, and, in particular, to the creation of ground-level ozone.
  2. Once upon a time, the U.S. EPA required that gas pumps in some urban areas have vapor-recovery nozzles.  These were designed to collect the gasoline vapors that would otherwise just pour out of your car’s gas tank as you refilled it.
  3. By and large, these were only mandated in areas that could not meet federal air pollution standards for ground-level ozone.
  4. But by 2006, virtually all new cars and trucks were equipped with on-board vapor recovery systems.  They collected their own gasoline vapors during refueling, stored them, and burned them
  5. In 2012, the EPA dropped its requirement for vapor-recovery nozzles (reference).  At that point, so many cars had the new on-board systems that the vapor-recovery nozzles no longer offered sufficient benefit to justify their cost.
  6. Whether or not gas stations were required to keep up those vapor recovery systems was left up to the states.  For example, Virginia chose to decommission all those vapor recovery systems in 2017 (reference).

The upshot is that gas pumps in my area haven’t had those vapor-recovery nozzles for more than half a decade.  They still have some sort of rubber cup on the fuel nozzle, but I guess that’s just to prevent splashback or possibly to aid the car’s own on-board recovery system.

Some implications

With this, a lot of things now click into place.

Vehicle fuel tank filler necks now have an elastic seal in them.  I’m sure that older cars did not have those.  That seal is required on a modern car because the on-board vapor recovery system needs a tight seal against the gas nozzle.  That’s the only way to make sure that the gas vapors in the tank end up in the on-board charcoal canister.

The standard advice of “Don’t top off your tank” now has a new rationale.  In the ancient past, that was the advice because gas expands as it warms, and if you topped off your tank in summer, you’d end up spilling gas out the fuel filler as you drove down the road.  Now, that advice is there to protect your on-board vapor recovery system.  If you top off you tank, you can end up shoving liquid gasoline into your vapor recovery system, something it was not designed for.

My old two-gallon gas can produced four gallons of gasoline vapors before I even considered spills, venting, and the gasoline-permeability of the plastic.  Every time I filled that at the gas pump (since 2017), that displaced the two gallons of vapors, in the gas can, into the atmosphere.  And then, as I repeatedly filled the tank on the mower, that sums up to another two gallons of gasoline vapor displaced into the atmosphere.

How does that compare to gasoline vapor emissions from cars?

The EPA estimates that these on-board vapor recovery systems capture about 98% of gasoline vapors, at least according to this presentation.  The same source shows that the EPA estimates an average of 0.32 grams of gasoline spilled per gallon dispensed at a typical gas station.

The U.S. averages about 650 gallons of gasoline consumed per licensed driver.  Based on that, a year’s worth of fill-ups, for the typical licensed driver in the U.S., would generate:

  • 13 gallons of gas vapor spilled directly into the atmosphere (2% of that 650 gallons).
  • Another 12 gallons of gas vapor due to the average 208 grams of fuel spilled (0.32 g/ gallon).

In other words, the average driver with properly-functioning vapor recovery equipment and average diligence about spilling gasoline will generate about 25 gallons of gasoline vapors annually.

In that context, the 4+ gallons of gas vapor directly emitted by my old gas can seems quite material.  Particularly because my wife and I now exclusively drive her Prius Prime.  We seem to use on-order-of 40 gallons of gas a year, with the rest of our travel being electric.  From that 40 gallons, based on those EPA averages, we’d only be emitting about 1.5 gallons of gasoline vapor per year.  So that, in our household, the lawn mower and old gas can were responsible for far more gas vapor emissions than our car was.

That said, it’s worth noting that the lawn mower — even with the old gas can — is nowhere as bad as the average American passenger vehicle, in terms of venting gas vapor to the atmosphere as a result of refueling.  That’s not because the lawn equipment is clean — it’s not.  That because the average driver uses such a vast quantity of gasoline.  Even those small fractional losses during refueling add up to far more gasoline vapor than the lawn mower / old gas can emit in a season.

But that’s only for refueling-related gasoline vapor losses.  That does not include any gasoline vapor losses by the mower during operation.  For example, losses through the charcoal-filled gas cap, losses from the vented carb bowl after engine shutoff, and so on.  I still need to track those down.

The new gas can ought to eliminate half of those “displacement” gas vapor emissions.  The new can vents through the end of the pouring spout, so it’s “inhaling” the gas fumes out of the tank as it puts new gas into the tank.

The only gas vapor that will be directly emitted as a result of displacing vapor during refueling will be from refilling the gas can, at the local gas pump.  That, because our gas pumps no longer have vapor-recovery nozzles.  And apparently haven’t had them since 2017.

Post #1773: Gas vs. electric mowing, part 3: Why do all gas cans suck?

Source:  ACE Hardware.

I’m not the sort of person to buy something new, when the old one still works.  But my deep dive into lawn mowers and air pollution has convinced me to buy a new gas can, shown above.

There was nothing wrong with my current gas can.  In the sense that it worked exactly as it did when I bought it about three decades ago.

But technology that was fine three decades ago doesn’t really cut it in the modern world.

In this post, I’m going to explain why I took this momentous step. Continue reading Post #1773: Gas vs. electric mowing, part 3: Why do all gas cans suck?

Post #1722: Gas versus electric lawn mowing, part 2: The information you seek is not available.

 

Husqvarna versus Hummvee.  The one on the left is the true environmental bad guy?  Really?  Who says so?  And how do they know?

This post is the second in a series tracking down the origins of this generic statement:

  • One hour of mowing your lawn using some gas-powered lawn device
  • produces as much something-something-something
  • as 200 or 300 or 350 miles of driving something.

The information you requested is unavailable.

A good overview of this issue can be found on The Straight Dope.  Note how old that is — that posting dates to 2010.  Clearly, many variants on this one-mower-hour-equals-300-miles theme already existed at that time.  That posting specifically notes that all of the information behind that claim was made obsolete in 2012, when the EPA issued new standards for pollution from small engines.

And yet, we still see that exact same language today.  It was one hour equals 300 miles (say) 20 years ago.  And it’s the same today.  Despite the 2011/2012 EPA regulations limiting small engine pollution (Source:  EPA).  And despite two decades of changes in passenger vehicle technology and mix of vehicle types.

I get my first clue about the loosey-goosiness of this mower-versus-car statement from the California Air Resources Board (CARB), which currently says (emphasis mine):

Today, operating a commercial lawn mower for one hour emits as much smog-forming pollution as driving a new light-duty passenger car about 300 miles

Based on that critical word — commercial — maybe the commonly-cited one-hour-equals-300-miles statement has little to do with my 21″ Husqvarna mower with its Honda GVC-160 engine.  It was based on … something else.

And as I dig deeper, I’m beginning to understand why I couldn’t find any details on what these lawn-mower-versus-car statements actually mean.  After some hours of internet search, I can find authorities such as CARB that make those statements.  But I can find absolutely nothing on the details behind those statements.

In short, I know what CARB said, but I still know nothing.  I have no idea what CARB means by:

  • “a commercial lawn mower”, or
  • “a new light-duty passenger car”, or
  • “smog-forming pollution”.

As far as I can tell, CARB provides no details whatsoever.  Or, at least, none that I can find on their website.  Do they mean operating the equipment in a typical use-case, or do they mean running it full throttle, flat-out?  Do they mean a new piece of equipment, or the average mower currently in use.  How big is a commercial mower?  Does “passenger car” include SUVs or not?  Did they use a specific passenger car, such as a Prius?

And I still don’t know how to scale it down to my actual, as-used 21″ lawn mower.

Even worse, after looking into the regulations, I may never know how much pollution that mower emits.  That’s because U.S. regulations appear to be stated in terms of maximum limits, when the engine is run through a pre-defined duty cycle.   As far as I have been able to tell, nobody publishes the actual as-measured data on actual engine use.

Can you derive that statement from the regulations?

Now things get really nuts.  Even if I can’t find data on actual emissions, I ought to be able to find information on emissions limits for small engines and cars, and compare them. 

And I can do that.  The only problem is, if I do that accurately, with modern emissions limits, that makes small engines appear vastly worse than the one-hour-equals-300-mile meme suggests.

Let me start with my lawn mower, with a Honda GCV-160 engine, displacement of 160 CC or 9.8 cubic inches, rated for 4.4 horsepower or 3.3 KW.  All of that is per Honda.

Next, the EPA standard for “Class I” small portable engines is 10 grams of NOx and exhaust hydrocarbons per engine KWH per hour.  So, for the Honda engine rated at 3.3 KW, the EPA would appear to allow 33 gram per hour, combined NOx and exhaust hydrocarbons, under its mandated duty-cycle testing.

But the EPA standard for cars (shown here) works out to new-fleet average of just 0.03 grams of NOx and exhaust hydrocarbons per mile, for all passenger vehicles.

When I put those together, the exact statement appears to be that for one hour of running my Honda-powered lawn mower, the EPA allows that mower to release as much N0x and unburned hydrocarbons as (33/0.03 = ) 1100 miles of driving, by the average new gasoline-powered passenger vehicle.

I think I understand why I get such an extreme answer.  I used the modern (Tier 3) emissions standards for cars.  Those only went into place around 2017 or so.  Whereas these statements about mowers-versus-cars originated much earlier.   If I track down the Tier 2 standards for cars, and use the cleanest “bin”, the standard calls for no more than 0.125 grams NOx and unburned hydrocarbons per mile.  For that standard, the maximum allowable NOx and unburned hydrocarbon emissions from one hour of mowing equal the allowable emissions for (33/.125 =) ~250 miles of driving a typical passenger car at the maximum allowable Tier 2 emissions.

So it appears plausible that the one-hour-equals-300-miles statements derive from comparing maximum allowable levels of smog-producing exhaust emissions.  And that if anyone bothered to update those old statements to the current (Tier 3) car standards, they could make an even more extreme statement.

But.  But those are the upper limits on what is allowed.  They aren’t the actual emissions.

And none of that squares with the current CARB statement cited above.  For CARB to make that one-hour-equals-300-miles, they had to specify a commercial (presumably, large) lawn mower.

So I now think I understand how you could come up with that statement.  But I’m still not quite sure whether that statement reflects the real-world outputs of those pollutants.

Still, it remains plausible that a small lawn mower engine really is that “dirty”, by modern car standards.  The EPA estimates that modern vehicles produce about 2% of the smog-forming pollutants that (say) 1960s-era vehicles did.  And, basically, lawn mowers are still back in the 1960s in terms of pollution controls.  Catalytic converters, sealed fuel systems, exhaust-gas regeneration — all of those pollution controls are standard on cars, and unheard-of on lawn mowers.

In any case, I’m going to keep digging.  Somewhere, somebody should be able to show actual measurements of emissions of a modern lawn mower, in a form comparable to emissions measured for a modern car.

Post #1721: Gas versus electric lawn mowing, part 1: The conundrum

 

Preface:  I was an early adopter of electric lawn mowing.  Early, in this case, being somewhere around 1995, well before battery-powered electric mowers existed.  But after a couple of burnt-out mowers and many trashed extension cords, I gave up and bought an efficient gas walk-behind mower. 

That was circa 2015, and I have not looked back.  Until now.  This is the first of a series of posts looking at gas versus electric lawn mowing.

Part 1:  The conundrum

I keep reading ever-more-outlandish statements about just how much pollution gas lawn mowers generate.  Depending on which source you read, you will come across this generic format:

  • One hour of mowing your lawn using some gas-powered lawn device
  • produces as much something-something-something
  • as 200 or 300 or 350 miles of driving something.

Weirdly enough, it’s always one hour.  Everything else varies from source to source.  In addition, I am not the only person to have noticed that these car-versus-mower statements are all over the map.  This has gotten to the point where the EPA apparently doesn’t support statements like this any more (reference).

I’m sure there’s some truth in there, somewhere, but that has the look of a standard advocacy statement.  Typically, if you take one of those apart, you’ll find that somebody has purposefully created a worst-possible-case-vs-best-possible-case contrast.  Statements like that are crafted to convince rather than to inform.  And that’s done with forethought,  in pursuit of some presumed policy or economic goal.

Worse, as variants of that get tossed around, further and further from the actual research, they start to take on urban legend aspects.

Let’s play “spot the loony”.  Consider this statement, from an otherwise reputable source, Family Handyman magazine:

One hour of running a gas mower emits as much carbon dioxide as driving a car 300 miles, ...

That’s obviously a mistake.  Carbon dioxide (C02) emissions are directly proportional to the amount of gasoline burned.  Each gallon of gas generates about 20 pounds of C02 (Source:  EPA).  The average new (2021) U.S. passenger vehicle, including electric and plug-in cars, gets less than 25 MPG or equivalent (Source:  EPA).  Taken literally, the statement above says that a lawn mower burns (300/25 =) 12 gallons of gas per hour?

Must be one hell of a lawn mower.  Big agricultural combines (as above) can easily have that level of fuel consumption.  But not your typical 21-inch 3.5 HP Briggs and Stratton lawn mower.

My wife confidently informs me that we burn two gallons of gasoline per year, cutting our grass.  She’s confident because a) she mows the lawn, and b) she hates putting the gas can in her car.  So she’s sure she does that once per season.   This, on a half-acre suburban plot, less the footprint of house, driveway, and landscaping.

By contrast, for cars, in the U.S., we burn an average of about 650 gallons of gasoline per licensed driver per year (Source).  For me and my wife, if we were average, we’d be burning 1300 gallons of gasoline per year, in our car. (We aren’t — we drive a Prius Prime and arguably use about 40 gallons of gas per year in that.)

Plus two more gallons, for the lawn mower.

So there’s the conundrum.  Where does this gas-lawn-mower-as-environmental-horror-story come from, given how little fuel the typical suburbanite consumes for lawn mowing, compared to driving?

For sure, the carbon footprint of our gas lawn mower is rounding error in the context of total household fossil fuel use.  Not because small gas engines are any great shakes.  Simply because the fuel used to mow the lawn is negligible.

For perspective, using Virginia’s power generation mix (0.65 lbs C02 per KWH), two gallons of gasoline generates as much C02 as 60 kilowatt-hours, or roughly 160 watt-hours per day.   Based on these typical wattages, the gas lawn mower has the same carbon footprint as the following daily use of these home appliances:

In short, for my primary environmental concern — global warming — mowing the lawn just doesn’t matter.  Or, it matters less than many other common activities of daily living, such as washing dishes or watching TV.

But I still would like to know the full story here,  Given the small amount of gasoline consumed, how closely does whatever-it-is that is the underlying research actually apply to my situation?  Should I consider early retirement for my gas lawn mower, in favor of battery-powered?  Should I plan on buying a battery-powered mower if and when my current one dies?

I already know some of the answers.

Briefly:   First, the horror story is about smog (not carbon footprint).  Second, it focuses on major small-engine consumers of gasoline.  The total environmental impact appears to have been estimated based on consumption of 3 billion gallons of gasoline annually, for lawn and garden equipment.  With lawns surrounding roughly 100 million U.S. households, that works out to about 30 gallons of gas, per lawn, per year.  Or about 15 times the rate at which my mower uses gas.

The upshot is that I’m not deeply concerned about this.  But I would like to know more.  The rest of the posts in this series will dig a little deeper into this, including (if possible) finding the original EPA research that has spawned this class of gas-lawn-mower-bad advocacy statements.

More to come.  It’s a nice day.  I’m going to go work in the yard now.

Post #1714: Ah, crap, another 80 MPG trip.

 

I am presently recovering from a severe shoulder sprain.

It was self-inflicted, the result of patting myself on the back too hard.

The problem starts with my wife’s Prius Prime.  It has more-than-met our expectations in every respect.  In particular, as-driven, it typically exceeds the EPA mileage rating, either on gas or electricity.

Lately, I’ve been trying a few techniques to try to squeeze some extra gas mileage out of the car.  Just some around-town trips, driving it to try to keep the gas engine in its most efficient zone.  Which, per Post #1711,  boiled down to fast starts on gasoline, followed by coasting on electricity.  Below, that’s an attempt to stay on the top of the green efficiency “hill”, followed by keeping the gas engine off while driving in the aqua “EV carve out” zone.  (The labels on the contour lines are “efficiency”, the percent of the energy in the gasoline that is convert to motion.)

Results were encouraging.  A couple of test trials showed mid-70-MPG for a series of trips and test runs, entirely on gasoline (using no grid electricity).  Given that the car has an EPA rating of 55 MPG for city driving, I figured I was doing something right.

But at some point, it dawned on me that

  1. the current EPA mileage test is based on the typical U.S. driver (i.e., somebody who drives like a bat out of hell, whenever possible), and
  2. I have no idea what my “typical” city mileage is, because I almost never drive the car, around town, on gasoline.

In short, I made a classic mistake of trying to do an experiment without a control.  I had no baseline to which I could compare my results.  I literally didn’t know what mileage the car would get if I wasn’t fooling around with the accelerator pedal.

I decided to find out.  Yesterday we took a trip out to my sister-in-law’s and back.  About 15 miles, mostly on 35 MPH suburban roads, rolling hills, no traffic to speak of.  Gas only.  Didn’t need the AC or the heat.  Relatively few stop lights.  Driving normally.  (But acknowledging that I’m a light-footed driver by nature, and that monitoring the car via a Scangauge 3 has done nothing but increase that tendency.)

In short, reasonably close to ideal conditions for a trip.

Results:  The odometer clicked over to 80 MPG for the trip, just as we were returning to our driveway.

I am reminded of the following medical advice:  If untreated, the common cold will last a week.  But with proper medical attention, you can expect a full recovery in just seven days.

Thus it would appear, for urban hypermiling in a Prius Prime.  As-driven, 80 MPG, for my suburban area.  No fancy footwork required.

Post #1713: Norfolk Southern Accident History

 

As we all know by now, the cause for the recent Ohio train derailment was traced to an overheated, failed wheel bearing, per the National Transportation Safety Board.

Sounds like a random equipment failure that, in this case, had some bad consequences.

But isn’t that just part of a much larger pattern of neglect, leading to an ever-increasing rate of train derailments?

No.  And that’s easy to say, because, of course the Feds track this.  Of course you can access it.  You just need to bother to look.

From the Federal Railroad Administration, Office of Safety Analysis, Ten-year query form.  Data for 2022 are preliminary through November.

Norfolk Southern’s rate of derailments has been more-or-less the same over the past two decades.  Same for accidents involving hazardous materials.

Obviously, facts cannot possibly compete with the angertainment-fest that has become our national news reporting.  As evidenced by the comments sections on newspaper articles.

But on the off chance that you might have been wondering about this, the answer is no.  For Norfolk Southern, the rate of accidents of this type is about what it has been for the past twenty years.

Post #1712: The Balkanization of EV battery recycling

 

Background:  I can’t get rid of the damned thing.

My wife and I have been believers in electrically-powered transport for some time now.

In 2008, we bought an aftermarket battery pack to convert my wife’s 2005 Prius into a plug-in hybrid electric vehicle.  At the time, the manufacturer (A123 systems) assured us that the battery pack would be fully recyclable, and that they had partnered with Toxco, Inc. to guarantee that.

To be honest, that retrofit never worked very well.  It wasn’t the battery’s fault.  The main limitation was that a Prius of that generation wasn’t really built to function as an electric vehicle.  That placed a lot of limitations in driving in all-electric (“EV”) mode.  Gasoline savings were modest, at best.

Fast-forward to 2012.  A123 had gone bankrupt.  Toxco was no longer in the battery recycling business.  We had a problem with the charger on that battery pack, and decided to have it fixed, in large part because, at that time, there was no way to get rid of the damned thing.  Far less hassle to fix it and keep using it.

At that time, the word was that infrastructure for EV battery recycling was just around the corner.  But from a practical perspective, here in Virginia, we couldn’t find someone to take that off our hands and recycle it.

Fast forward to 2018, and the original nickel-metal-hydride traction battery in that Prius died.  We thought about scrapping the car at that point (177K miles), but everything else was fine, we dreaded the thought of buying a new car.  So we we paid to have the dealer install a new Toyota nickel-metal-hydride (NiMH) traction battery.  (Toyota recycles the dead NiMH batteries recovered through their dealerships.)   But, in part, the decision to keep the car was driven by that A123 battery pack.  We looked around for recyclers, but there was still no way to get rid of the damned thing.

Apparently, EV battery recycling was still just around the corner.

Jump to 2023.  It now looks like that 15-year-old A123 pack has finally given up the ghost.  It will no longer charge.  And at this point, we have no interest in trying to get it fixed, even if we could.  Any money spent on that would be better invested in getting a new purpose-built PHEV, such as a Prius Prime.

I’m sure you’ve guessed the punchline.   I just looked around for recyclers, and yet again, there is even still no way to get rid of the damned thing.

Now, that’s not 100% true.  There’s an on-line ad for a company that, if I give them all my information, might be willing to offer me a quote on how much they’ll charge to recycle my particular battery.  There might be a shop as close as North Carolina that might take it, if I could prepare it properly.  I haven’t bothered to inquire.  My wife’s going to call the dealer who installed it originally, after this three-day weekend, and see if they’ll remove it and dispose of it for us.  (Last time we asked, that wasn’t an option.)

My point is there’s no place within, say, 200 miles, that I can just call up, make and appointment, and drop off the battery for recycling.  It’s all either a custom, one-off service, or requires crating and shipping the battery, or required driving at least hundreds of miles, round-trip, if I can find a place that will take it.

On the plus side, I’m in no hurry.  A fully-discharged lithium-ion battery isn’t a fire hazard.  I’ve checked several sources on that, and that’s the overwhelming consensus.  A completely discharged lithium-ion battery is just dead weight, not a death trap.  You definitely don’t want to try to recharge one and power it up, once it has been over-discharged, as it can easily form internal short-circuits in an over-discharged state.  That can lead to a big problem in a short amount of time.  (And chargers in general will not allow you to try to charge a lithium-ion battery with excessively low starting voltage, for exactly this reason.)  But as long as you don’t do anything stupid — don’t bypass the charger, don’t puncture it, don’t roast it — it’ll remain intert.

On the minus side, it looks like the U.S. EV battery recycling industry is in no hurry, either.  I sure don’t perceive a lot of forward motion since the last time I looked at this.  Worse, what seems to be happening is that the industry is going to get split up along manufacturer lines.  Tesla will recycle Tesla batteries, Toyota will recycle Toyota batteries.  And if you fall into the cracks — with some off-brand battery — there will still be no way to get rid of the damned thing.

My impressions of the EV battery recycling market

I’ve been tracking this market for more than a decade now.  With the personal stake described above.  I thought I might take a minute to offer my observations.  In an unscientific way, without citation as to source.

First, it doesn’t pay to recycle these.  At least, not yet.  That was surely true a decade ago, and my reading of is that it’s still true.  So you’ll see people talk about the tons of materials saved, for ongoing operations.  But I don’t think you’ll hear anybody say what a cash cow lithium battery recycling is.

Second, EV battery recyclers start up and fail at an astonishing rate.  Near as I can tell, none of the companies involved in it, when I looked back in 2012, are still in that business.  I just looked up a current list of companies that cooperate with GM dealers for EV battery recycling, and all the names were new to me.  This “churning” of the industry has been fairly widely noted by industry observers.

Third, we’re still just around that damned corner.  The Biden infrastructure bill appears to have about a third of a billion dollars earmarked for development of EV battery recycling (source).

But surely you realize what that means.  See “First” above.  The fact that the Feds have to subsidize EV battery recycling is pretty much proof that it just doesn’t pay to recycle these big lithium-ion EV batteries.  At least not yet.

Finally, car markers are developing their own captive recyclers, for their own batteries.  Tesla has its own systems.  GM has contracts with a limited number of vendors, plausibly to serve GM dealerships.  Toyota has its own system, for batteries recovered by its dealerships.

That last move makes perfect sense.  Because recycling is a net cost, and yet a significant consumer concern, manufacturers are pledging to take care of their batteries, if they are recycled via their dealers.  But, so far, I’m not seeing any generic recycling capability for (say) any hybrid or EV showing up at a junkyard.  Let alone for my oddball A123 batteries.

Per this article, it currently costs Tesla more than $4 per pound to recycle its lithium-ion batteries.  At that cost, you can see why they might be willing to deal with their own, but they’re sure not going to take anybody else’s batteries for recycling.  It’s not clear that other processes — with less complete recycling of all the materials — are as costly as Tesla’s.  As of 2021, at least one company was in the business of simply warehousing used EV batteries on behalf of vehicle manufacturers, handing batteries replaced under warranty.   The theory is that right now, it’s cheaper to store them and hope for lower recycling costs down the road (reference).

I’m sure that big junkyards and scrap yards have some way of dealing with these, at some cost.  Surely plenty of the (e.g.) Generation 3 Toyota Prius hybrids with lithium-ion batteries have now been scrapped.  I don’t know if they can recycle via Toyota’s internal system, or if … well, I just don’t know.

Conclusion

All I know, at present, is that if I can recycle that totally dead 5 KWH A123 lithium-ion battery pack, it’s going to be either a hassle or a major expense or both.  As long as I can get it recycled, I will.

But, the fact is, until that 2005 Prius actually dies, I won’t have to face up to it.

And, in a nutshell, that characterizes the American market for lithium-ion EV battery recycling.

I’ve decided just to let that dead battery be, and let the 2005 Prius continue to haul around that 300 extra pounds of dead weight.

Because, as we all know, readily-available EV battery recycling is just around the corner.

Post #1711: State-of-charge hypermiling and a generalized theory of pulse-and-glide

Why pulse-and-glide saves gas.

Gasoline engines run most efficiently when under a fairly heavy load.  Load them too lightly, or too heavily, and their efficiency drops.

Below is the “efficiency contour” of a hypothetical 2 liter Atkinson cycle engine. Engine RPM is on the X-axis.  Engine load (output) is on the Y-axis.  The labels on contour lines are percents, and show the fraction of the energy in the gasoline that is converted into motion by the engine.  Those contour lines define a sort of hill, with the peak of the hill — maximum efficiency — occurring when this engine is running around 2500 RPM, putting out about 100 horsepower. And converts just shy of 39% of the energy in the gas into usable power.

Source:  Kargul, John & Stuhldreher, Mark & Barba, Daniel & Schenk, Charles & Bohac, Stanislav & McDonald, Joseph & Dekraker, Paul & Alden, Josh. (2019). Benchmarking a 2018 Toyota Camry 2.5-Liter Atkinson Cycle Engine with Cooled-EGR. SAE International journal of advances and current practices in mobility. 1. 10.4271/2019-01-0249. Accessible though this link.

The engine modeled above is a 2.0 liter Atkinson-cycle engine.  That’s just a bit bigger than the 1.8 liter engine that’s actually in the Prius Prime.  But it’s close enough.

Below, there’s the crux of the problem.  Much of the time, the engine is inefficiently lightly loaded.  I’ve marked the power required to cruise on level ground at a steady 55 MPH in a Prius.  The car only needs about 12 HP.  (I infer this from the ~12 KW of power drawn to keep the car at that speed in electric (EV) mode.   That power, less about a 20% loss in the electric motors, is the energy required at the wheels to keep the car moving forward at that speed.

And so, if you cruise along at a steady 55 MPH on the gas engine, even though the car won’t be burning a huge amount of gas, what little it burns will be burned inefficiently.

Instead of running that engine steadily at 12 HP output, you could alternatively run it hard — run it briefly at 100 HP — then shut it off.  And repeat as necessary.  That’s pulse-and-glide.

And that’s why pulse-and-glide saves gas.  You extract energy from gasoline as efficiently as possible, by running the engine under heavy load.  And then you match the engine output, to the average power required by the car, by cycling the engine on and off as needed.

Traditional pulse-and-glide makes you a rolling hazard.

With traditional (or kinetic-energy) pulse and glide, you first run the gas engine and speed up.  Then switch it off, coast, and slow down.  And repeat.

Practically speaking, this is of almost no value on the public highways, because this makes you a nuisance to other drivers.  It makes you into a rolling traffic hazard.

Potential energy pulse-and-glide requires the right terrain.

Speeding up, however, is not the only way to store the output of the car’s engine.  Going up a hill works just as well.  You store that excess output in the form of potential energy (height) instead of kinetic energy (speed).  Apply gas on the uphills, coast with engine off on the downhills.

I can attest that this most definitely works.  This is how I achieved my last two 80-MPG all-gasoline (no energy from the grid) road trips.

Needless to say, this only works where you have significant hills.  Ideally, hills large enough that the car will maintain the posted speed limit on the downhill with no or minimal energy input from the drive train.

A new/old concept:  State-of-charge pulse-and-glide.

Both methods described above can be done by a standard gas car.  No electric motors are required.  In fact, in a Prius, you achieve maximum efficiency under either method if you never use your electric motors.  (Using the gas engine to charge the battery, then run the motors, wastes about 30% of the power produced.)  Champion Prius hypermilers actually shift the car into neutral on the “coast” phase, specifically to avoid moving electric current into or out of the battery via the motor/generators.

But a plug-in hybrid electric vehicle (PHEV) like the Prius Prime has yet a third option, which I’m going to call state-of-charge pulse and glide.

To be clear, what I’m about to describe is something that the car does, on its own, anyway.  The only question is whether you can modify your driving behavior to take exceptional advantage of it.

If you use the gas engine to charge the battery, then run the electric motors, that wastes about 30% of the energy produced by the gas engine.  So, at first blush, it seems like you’d want to avoid using those electric motors.

But, if you charge that battery at the peak of the gas-engine efficiency curve, that means the electric motors are using up your gas with somewhere around (0.7*38% = ) 27% efficiency.

This leads to the section that I’ve labeled “EV carve out” above.  Roughly speaking, if the driving situation requires less than about 25 KW of power, it’s more efficient to run in EV (electric-only) mode, as long as you can later recharge the battery at relatively high engine load.  (So that the recharge happens near peak gas engine efficiency.)

In the Prius Prime, assuming this engine chart is a reasonable proxy for the actual Prime 1.8 L engine, that has the following practical implication for running the car in hybrid-vehicle (no-grid-power-used) mode.  If you can, you should run on electricity-only up to a current draw of about 90 amps.  That’s the point at which the electric motors, less their inherent 20% loss, are producing about 25 KW of power. That’s the point where switching to gas propulsion is more efficient.

But the closer you get to that 90 amp limit, the less advantage electricity has over gas, and the less gas you are saving.  So, from a battery wear-and-tear perspective, it’s probably best not to push it that far.  You will likely get the bulk of your savings with a more conservative limit of (say) 50 amps, or roughly a “2 C” discharge rate.  (The rate at which the entire EV battery would be dead in half an hour.)  Assuming the car will let you do that, in hybrid mode.

So, a conservative rule-of-thumb is that a power output of somewhere around 17.5 KW (25 HP) is where you should try to flip the car from gas to electric and back.

To be clear, the car does something like this on its own.  At low power demands, it shuts off the gas engine and used the electric motors.

What I have noticed, however, is that there’s considerable hysteresis in the car’s decision.  In particular, once the gas engine is on, it tends to stay on until power demand gets quite low.

So I believe that driver intervention can improve mileage, using (e.g.) terrain anticipation.  If you’re coming to a stretch of road with likely low power demands — cresting a hill, starting a slow deceleration, or just coming up to a level stretch — you may be able to beat the Prius’ internal algorithms.  Conversely, when you see a high-power-demand situation coming up — a hill, say — you can flip the car into gas mode before it begins to bog down in electric mode.

My simple initial rule-of-thumb will be a 50-amp cutoff.  When in hybrid mode, drive the car on the electric motors up to 50 amps current or low state-of-charge cutoff, whichever comes first.  Anything over 50 amps, nudge the accelerator to kick the car into gas mode.

Edit:  I decided to do a little acid test of the concept.  As every driver knows, the worst trips for a gas engine are short, around-town jaunts.  I decided to do a little run to a couple of stores, in hybrid vehicle mode, total trip of about 8 miles, divide into three legs with stops in-between.  After the mandatory gas-engine warm-up period, whenever the gas engine came on/power was needed, I loaded the gas engine heavily.  I gave it enough throttle to bring it immediately to the “power” zone on the dashboard.  But, once up to speed, I let off the accelerator to shut the gas engine off, and drove for as long as feasible on electricity only, respecting a maximum draw of 50 amps.

Results:  71 MPG.  And it was clear that if I’d had a longer distance between stops, that would have increased. 

One short trip does not prove the concept.  And the Prius chastised me soundly for those hard accelerations, basically giving me a flunking score on the eco-meter.  Nevertheless, I consider this first test to be encouraging.

By the book, and by the dashboard readouts, I was doing everything wrong. And yet, it’s hard to argue with the MPG.

Edit 2, 2/19/2023.  Not so fast.  Building on the above, I went to a local disused office building and circled the parking lot.  Roughly a 1.3 mile circuit, 25 hour speed limit, three full stops per loop.  On one set of loops, I tried this hypermiling approach.  On another set, I drove gently, then used the “charge” function to bring the battery state-of-charge back to its original level. 

Results:  In both cases, I got about 75 MPG.  Which, in hindsight, may simply be what the Prius Prime gets, driven in hybrid (gas-using) mode, around 25 MPH.

I think the moral of the story is that I’ve done so little around-town driving in hybrid (gas-using) mode that I’m not sure sure what sort of gas mileage I should expect as a baseline.

Conclusion

Anyone who has ever used the Prius cruise control in hilly country knows that it’s quite “reactive”.  It doesn’t anticipate the hills, but instead holds speed steady, then pushes the car far out onto the power curve in an attempt to maintain speed on the uphill.  For that reason alone, I don’t use the cruise control on hilly roads, as I feel that I can drive the car more efficiently in manual mode, making some modest adjustments in speed on the downhills and uphills.

Similarly, I’m betting I can squeeze a little extra mileage out of the car, in hybrid mode, by manually selecting the point of switch-over between gas and electric propulsion, and pushing the gas engine at high load to maximize efficient use of gasoline.  Then, once at speed, or over the crest of a hill, lifting my foot off the gas briefly to shut the gas engine down, and continuing in electric-only mode as feasible.

You need an extra bit of instrumentation to be able to do that well.  I’m using a Scangauge 3, which will show me quantities such as battery current, engine RPM, and engine output.

What makes this work, as a form of pulse-and-glide, is, of course, the traction battery.  That’s where the excess power production of the gas engine is stored if not needed.  So the right way to view this is state-of-charge pulse-and-glide.  Instead of letting the speed vary (kinetic energy), or the height vary (potential energy), you let the battery state-of-charge vary (electrical energy).

Same concept either way, you just choose a different place to store the excess power output of well-loaded gas engine.  With different implications for how usable pulse-and-glide is, in actual highway traffic, for a given terrain.

Finally, I note that there have been recent patents issued for systems that would automatically pulse-and-glide large trucks, based on a system that anticipates changes in terrain.  They seem to be characterized as a more fuel-efficient form of cruise control.  With everything in modern cars being controlled by a computer, it doesn’t seem too far-fetched to think that some form of automated pulse-and-glide — a fuel-saving cruise-control mode — might eventually become a standard option on vehicles capable of doing it.

With that point of view, driving a gas engine at a constant, low engine load is something of a relic of the past.  It dates to the era when there was literally a metal cable connecting your gas pedal to the throttle body on the carburetor.  With everything computer-controlled these days — and carburetors a thing of the far distant past, for cars — it doesn’t seem like a stretch to ask your computer to do your energy-saving pulse-and-glide for you. As long as you have some safe way to store that excess gas-engine output.