Bus Fuel Economy

Hank Seiffhseiff@cleanvehicle.orgDecember 6, 2007

What Do We Really Want? - Miles Per Gallon - Petroleum Miles Per Gallon - Miles per Dollar - Vehicle Total Costs vs Vehicle

Operating Costs

Bus Fuel Economy

For most of this presentation, let’s assume we start with an “ordinary” (non hybrid) natural gas or diesel

bus and want to maximize its MPG

Potential Ideas• Slow down, if possible• Lower HP• Look at engine BSFC curve• Better transmission/drivetrain match• Low rolling resistance tires• Wide based singles• Tire pressure • Low HP Engine Accessories• Aerodynamics• Less idling• Lower tare weight• Synthetic lubricants• Drive more gently• Hybrids• Alt fuels• Additives/ mileage enhancers• How to test for fuel economy improvement

Slow Down!

Potential Benefit: 2.2% mpg loss for every mph over 55

Problem: Transit and school buses don’t often go that fast

Lower HP Engine

Potential Benefit: - Better FE???- Lower Vehicle Cost

Potential Problems: - Driver Complaints- Longer Route Times

Look at BSFC Engine Curve

Diesel engine Brake Specific Fuel Consumption Curve from Heywood, “Internal Combustion Engine Fundamentals”

Lesson: Lower RPM = better fuel economy

100 N-m = 74 lb-ft HP= (Torque X RPM) / 5252

1 hp = 0.75 kw

Look at BSFC Engine Curve

Moral:

Lesson: Lower RPM = better fuel economy

Better transmission/drivetrain match

Potential Benefit: - Better FE – transmission should allow operation of the vehicle near “low-RPM, high MPG, sweet spot“

- Lower noise level

Potential Problems: - Driver Complaints

Lower Rolling Resistance Tires

Potential Benefit: - 2-3% Better FE- Benefits at all speeds

Potential Problems: - Are they available for transit buses?

- Initial Cost?

Wide-Base Singles in place of DualsPotential Benefit: - 2% Better FE

- Lower initial cost- Lower Weight

Potential Problems: - Are they available for transit buses?

- No reserve if tire fails

Tire Pressure

Potential Benefit: - 10 psi drop increases rolling resistance by 2% & FE by 0.5-1.0%

- Longer Tire Life

Potential Problems: It’s a hassle!

Low HP Engine Accessories

Potential Benefit: - Improved FE?

Potential Problems: - How well do they work?

- Cost- Engine Warranty

Electric Fan Array from Engineered Machined Products: http://www.emp-corp.com/

Better Aerodynamics

vs.

Potential Benefit: - Better FE- Better Image

Potential Problems: - Real benefit at higher speeds

Less Idling

Potential Benefit: - Infinite MPG!- Zero Emissions- Better Image

Potential Problems: - Driver Complaints- Engine Restarts- “We’ve always idled

buses”

Sample Idling Regulations

Locale Max Time ExemptionsCA 5 min pass onboard or 10 min < boardingAtlanta 15 (25 if <32F) NG or electric vehicles (!)DC 3 (5 if <32F) none relevantNYC 3 min bus picking up/discharging passengersMA 5 min none relevantVA 10 – diesel, 3 – others none relevant

list from American Transportation Research Institute - seehttp://www.atri-online.org/research/idling/Truck_Idling_Regulations.htm

Lower Tare WeightPotential Benefit: 10% change =

5-8% change in FE

Potential Problems: - Are low tare weight buses available?

- Initial cost penalty?- Mitigates against Natural Gas!

Synthetic LubricantsPotential Benefit: - Engine Oil 1.5%

- Axle and Transmission 1.5%- Longer change intervals- Longer component life

Potential Problems: - Increased Lubricant Cost

Driver Training – “Drive Gentle”Potential Benefit: - 5-20% FE

- Better Image- Longer Vehicle Life

Potential Problems: - Route Times- “You can’t drive a transit bus like that!”

Hybrids Natural Gas or Diesel

Potential Benefit: - 10-50% FE- Better Image- Lower Emissions

Potential Problems: - Initial Price Penalty (up to 75% increase!)- Battery Replacement

Alternative Fuels (NG)

Potential Benefit: - Up to 100% Petroleum Replacement (NG)- Government Alt Fuel Rebates- Lower Fuel Costs (at least for NG)- Improved Image

Potential Problems: - Initial Price Penalty- Fueling & Maintenance Facility Costs- Actual MPG likely poorer

Alternative Fuels (NG)• Cost (Alternative Fuels Index 11/30/07) before

tax:– Diesel - $2.72/gallon– NG - $1.64/DGE

• Cost (CVEF 8 Transit Fleet Survey 11/07)– Diesel - $2.86/gallon– NG - $1.46/DGE

Natural Gas Cost BEFOREBEFORE $0.50/GGE (=$0.56/DGE) Federal

Rebate!

Additives/Mileage Enhancers

For Instance: - Oil & Fuel Additives, - Magnetic Fuel Line Devices

Potential Benefit: - None -They don’t work!

Potential Problems: - Warranty Issues

- Cost

- Ridicule

How to Test for Fuel Economy Improvement

Uncontrolled Tests:

Controlled Tests:

Uncontrolled Tests• Same bus, different engines• Six buses with, six buses without• New “buy” of buses with new engine vs old buses

with old engineProblems:• Different drivers• Different buses• Different routes• Different seasons• Other variables• “Hawthorne effect”

Totally Controlled TestsProving Ground or Test Track with standard drive cycle

Avg

speed

6.9 mph

Avg speed

18.9 mph

Avg speed

12.3 mph

Semi-Controlled TestsSAE/TMC Tests on-road tests

Type I – two vehicles with component switched between runsType II – when it’s not possible to run two or more test

vehicles simultaneously; uses “control vehicle”Type III – components can be switched from one vehicle to

another in a short time Type IV – can use similar vehicles in revenue service

- information available from SAE or ATA’s Technology & Maintenance Council

Call for HelpHank SeiffDirector of TechnologyClean Vehicle Education Foundation703-534-6151hseiff@cleanvehicle.org