Download - Vehicle Efficiency Pathways
1
Vehicle Efficiency Pathways
How modern passenger cars are removing themselves from the environmental debate
John Bucknell
GM Powertrain
219 April 08
Abstract
Modern passenger cars must respond to market demand and regulation forces, delivering superior air quality, utmost safety and ever-higher energy efficiency. This lecture will discuss efficiencies on both the supply and demand pathways for improving energy efficiency in the context of emissions and safety regulations. Well-to-wheel and pump-to-wheel efficiencies will also be covered in brief to highlight the efficiency of Electric Vehicles
319 April 08
Topics Transportation Efficiency
State of the industry
Supply-side Efficiency Powertrain Efficiency Driveline Efficiency Load-leveling
Demand-side efficiency Aero, rolling-resistance, inertia
Electric Vehicles & Fuel-Cell Vehicles Pump-to-wheels, well-to-wheels
419 April 08
Market Economics Cost of ownership
Market demand has illustrated that customers will purchase what they can afford. Technologies that increase cost of ownership have great difficulty penetrating the market.
Energy Costs
Dual impact of increasing environmentalism and increasing energy costs have raised the visibility of vehicle efficiency.
Low energy cost of petroleum products has been the primary factor that has driven the market into a near monoculture for it’s energy needs.
519 April 08
Transportation Efficiency State of the industry
Economies of scale drive allow manufacturers to compete on cost. Any technology that cannot make a component at a minimum rate of one per minute requires additional sets of tooling, driving up investment and increasing the number of sales to break even.
Profit margins in the automotive industry are exceptionally small, as you’d expect with strong competition for a very large revenue stream.
State of the world has changed rapidly – developing new technologies that are sufficiently robust to be used by every consumer can take a decade or more. The industry is responding to the need for greater efficiency, vehicles on the market today are just the beginning.
619 April 08
Regulation Tailpipe Emissions
Air quality has been driven by the EPA and the California Air Resources Board. Details on how emittants are formed and regulated follow.
Passenger safety
Customer awareness of impact performance on standardized tests has driven the industry to achieve a minimum “Four star” rating in any test. The degree that of likelihood of injury to achieve the best rating has decreased significantly over the last ten years. High strain-energy density materials, and large masses of them have driven up body structure mass by about double in the same time frame.
719 April 08
Emission and Fuel Economy Test Cycles
819 April 08
Engine Fuel Balance
919 April 08
0
0.1
0.2
0.3
0.4
0.5
0 0.1 0.2 0.3 0.4 0.5
NOx Standard
HC S
tanda
rd
1983 Federal Tier 0
Federal Tier 1
History of Emission Control Standards
0
1
2
3
4
5
6
7
8
9
10
11
12
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
NOx Standard
HC S
tandar
d
Typical 1960 Vehicle (pre-control)
1971 California Std.1977 Federal Std.
NLEVLEV2
ULEV2
Emissions Standards 1960 to 2008
SULEV2
99.99%Reduction
1019 April 08
Exhaust Aftertreatment
Catalysts have the capability of modifying the reaction rates of chemical processes (typically increasing reaction rates) without being consumed while doing so.
The following chemical processes are of interest in automotive exhaust catalytic aftertreatment
• HC + O2 CO2 + H2O
• CO + O2 CO2
• NO N2 + O2
• These reactions proceed toward equilibrium at very slow rates at prevailing exhaust temperatures - catalysts increase their reaction rates to a degree that the exhaust aftertreatment becomes practical.
Conversion efficiency: (inlet concentration - outlet concentration)/inlet concentration
1119 April 08
SubstrateMat Can Washcoat Catalysts
Source: Corning (2001)
Essential Components of a Catalytic Converter
Substrate: a ceramic honeycomb-like structure with thousands of parallel channels for applications of washcoat and catalysts
Mat: Provides thermal insulation and protects against mechanical shock and chassis vibration
Can: A metal package encasing the catalyzed substrate and mat
Washcoat: a coating that increases the surface area of the substrate for catalysis
1219 April 08
Catalysts for Exhaust Aftertreatment
The active catalytic material is typically a blend of platinum, palladium, rhodium and nickel.
Small amounts of these materials are distributed on a alumina (Al2O3) washcoat, which is specially processed to have very high microscopic surface area. The high washcoat surface area helps to keep the catalytic material spread out to reduce the tendency to agglomerate and thus loose surface area.
Cerium oxide is often added to this mix to mechanically stabilize the alumina microstructure against thermal degradation.
Typically there are 0.5-2 grams of catalytic material per liter of overall catalyst volume, and the overall catalyst volume is about 50 ~ 80% of the engine displacement, depending on the application.
1319 April 08
Temperature Effects on Catalyst Capabilities
Catalyst efficiency at catalyst temperatures below 200oC is extremely low.
Catalyst efficiency rapidly increases as its temperature rises above 200oC and reaches its temperature plateau at about 400oC.
Light-off temperature: conversion efficiency reaches 50%
Current exhaust system design practice insures catalyst light-off within ~ 20 seconds without special aids. Catalyst heating devices in lowest emissions vehicles can achieve light-off in under 10 seconds.
Source: Heywood (1988)
1419 April 08
Catalyst Efficiency with Air/Fuel Ratio
Source: Heywood (1988)
Steady improvements in fuelling control, engine-out emissions and catalyst technology has made it possible to achieve 100% conversion rates of HC and NOx after catalyst light-off.
1519 April 08
Emissions SummaryFuel-burning engines create pollutants that are regulated - which are ever-more stringent. Emissions-control technology has evolved to the point where three-way catalysts are 100% efficient in converting HC, NOx and CO – only if the feedgas operates very close to stoichimetric air-fuel ratio.
Any lean-burning combustion process (Diesel or stratified charge) which improves fuel consumption also prevents catalytic NOx reduction by maintaining oxygen in the exhaust stream. Several technologies are emerging which consume fuel or reductant to purge Lean NOx Traps, at the cost of fuel consumption or added complexity.
1619 April 08
Supply-Side EfficiencyEnergy conversation pathway
Powertrain Efficiency (Stratified Charge/HCCI, Downsizing/Boosting)
Driveline Efficiency (Multi-speed Transmissions, CVTs) Load-leveling (stop-start, mild hybrid, series and parallel
hybrids)
1719 April 08
Energy Distribution in Passenger Car Engines
Source: SAE 2000-01-2902 (Ricardo)
1819 April 08
1919 April 08
Modern Naturally Aspirated Brake Thermal Efficiency Map
0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Fra
cti
on
Maxim
um
To
rqu
e
Fraction Maximum Engine Speed
Fra
ctio
n T
herm
al E
fficie
ncy
2019 April 08
Compression vs Spark Ignition
Compression ignition achieves significantly higher compression ratios than spark ignition – raising thermal efficiency
Spark ignition engines control load by throttling, introducing parasitic losses at less than maximum load which reduces thermal efficiency
Smoke limits reduce power density of diesel engines to only about 80% of energy density of spark ignited of similar displacement. High operating pressures require heavy construction which further lowers power/weight ratio
Source: Heisler (1995)
2119 April 08
Powertrain Efficiency Pathways- Engine -
Prior three slides show that the maximum fraction of fuel energy that reaches the brake is 30-40% of the fuel input energy, which is the most that thermodynamics allows.
Spark ignition engines pay a loss to reduce load by throttling – which is effectively operating a vacuum pump. Several technologies seek to reduce or eliminate pumping work:
• Exhaust Gas Recirculation (EGR) – load reduction by diluting incoming combustion air
• Variable valve timing (including cam phasers and variable lift/duration systems) – load reduction by reducing trapping efficiency and adding residual (internal EGR)
• Stratified Charge with unthrottled operation – load control via fuel mass running lean
• Homogeneous Charge Compression Ignition (HCCI) – load control via fuel mass and residual preventing lean operation
• Downsizing/Boosting – Reduction in displacement of engine so use of lowest efficiencies is mostly avoided and then boosting to enhance available load
2219 April 08
Powertrain Efficiency Pathways- Driveline -
Knowing that an internal combustion engine is most efficient in a limited regime, the driveline can be optimized to enable engine operation the least amount of time away from that regime.
• Multi-speed Transmissions – 6, 7, 8 speeds with ratio ranges from 5.0-6.0 give powertrain controller best option of matching engine to current power demand
• Continuously Variable Transmissions – Same as multi-speed transmissions, but typically have high parasitic losses
• Load Leveling – Through use of onboard energy storage (electric or other), energy conversion can happen at most efficient point in map. Hybrids achieve this through several different strategies – parallel, series or dual-mode are most-often discussed. Micro-hybridization also appearing due to low cost of implementation.
2319 April 08
Load-LevelingEngine Stop Start (ESS)
Eliminates fuel consumed during deceleration and idle
Fuel On
Fuel On
Fuel Off
Fuel Off
Source: SAE 2001-01-0326 (GM)
2419 April 08
Load-Leveling
Source: SAE 2006-01-1502 (GM)
Mild Hybrid
Regenerative Braking, Load-Leveling and Idle Stop
2519 April 08
Load-LevelingStrong Hybrid
Electric-only operation, Regenerative Braking, Load-Leveling and Idle Stop
Parallel, Series and Two-Mode e-CVTs
2619 April 08
Demand-Side Efficiency Not a true ‘efficiency’, however losses that are not
minimized could be considered ‘in-efficient’
Major Components
Inertia Loads (Kinetic Energy)
Aerodynamics
Rolling Resistance
2719 April 08
Demand-Side Efficiency Inertia Loads
Vehicle mass requires proportional power to accelerate. Vehicle duty cycles with greater time spent accelerating will be more sensitive to vehicle mass.
Aerodynamics
Pressure drag: The loss due to the difference in pressure on the front face versus the rear face of the vehicle. The dynamic pressure (also called stagnation pressure) on the leading face is a measure of the kinetic energy of the displaced air.
Friction drag: Losses due to viscosity effects are also substantial. Boundary layer theory says that particles immediately next to a vehicle must be moving at vehicle speed as compared to at the free stream velocity. The shear force created by the relative velocity of the fluid is proportional to vehicle speed and ‘wetted’ surface area moving through the fluid.
The two speed-dependent components cause aerodynamic drag to increase primarily with the square of vehicle speed
2819 April 08
Demand-Side Efficiency Rolling-resistance
Driveline: Seals, bearings, gears, CV and Cardon (universal) joints Any component using a viscous fluid to reduce contact stress
for increased durability also suffers the losses of viscous shear forces regardless of the load.
Brakes Friction brakes work by rubbing two components together.
Unfortunately due to the balancing of pad retraction and response time, disc brakes will drag the pads against the rotors – a little or a lot depending on the design. Drum brakes by their nature have very little hydraulic volume and thus can retract far enough to not drag.
2919 April 08
Demand-Side Efficiency Rolling-resistance
Tires Part of the suspension isolating the vehicle from surface
irregularities. Tire is both a spring and a damper, with greater spring rate and lesser damping force with lesser sidewall height. Spring rate is proportional to inflation pressure. Greater isolation drives greater sidewall and lower pressure.
Inflation pressure is same as tire contact pressure. Contact area is proportional to mass supported by the tire. The greater the contact area, the more rubber has to deflect as it tracks across the surface. Increased tire diameter decreases the degree of deflection. Rubber is not perfectly elastic, so some energy is lost.
The force to roll a tire is therefore proportional to the normal force and the volume of rubber deflected per second which is proportional to rotational velocity.
3019 April 08
Measuring Vehicle Efficiency EPA and real world fuel economy (Efficiency) is impacted by the
vehicle’s drag force. Drag is determined by taking a vehicle to 70 mph and then shifting into neutral and measuring speed versus time and thus deceleration rate. Knowing the mass of the vehicle, a drag force versus vehicle speed can be derived. This drag force data is fitted to a 2nd-order polynomial whose coefficients are published by the EPA – called the ABC coefficients.
The chassis dyno where emissions and fuel economy data is taken has Rollers instead of pavement, with vehicle strapped down Only drive-wheels turning No aerodynamic loading
The A,B,C coefficients determine the load which the dyno program must match over the course of the test cycle
3119 April 08
Vehicle Drag Force Example
A = 28.73 lbB = 0.7338 lb/mph
C = 0.01084 lb/mph^2
3219 April 08
Evidence of Vehicle Efficiency EPA data shows that there is no magic. Following slides show
every vehicle for sale in 2008 Model Year in the US.
3319 April 08
Inertial Loads
3419 April 08
Aerodynamics
3519 April 08
Rolling Resistance
3619 April 08
Downsizing
3719 April 08
Typical Mid-Size Vehicle Energy Distribution Idle 0.90
Engine Losses 5.97
Accessories 0.17
Driveline Losses 0.25
Aero 0.21
Rolling 0.34
Kinetic
Braking 0.45
Engine D/L 1.00 1.258.29 units
Urban Federal Test Procedure (FTP)
3819 April 08
FTP City – Mid-Size Sedan Simulation
3919 April 08
Simulation – Level of Hybridization
4019 April 08
Simulation – Hybrids with Downsizing
4119 April 08
Simulation – Advanced Powertrain Tech
4219 April 08
Electric Vehicles & Fuel-Cell Vehicles
4319 April 08
Well-to-Wheels and Tank-to-Wheels
Any true discussion of energy diversity and it’s impact on GHG must discuss the source of energy (ie the Well)
Electric Vehicles will receive the bulk of their energy from coal-fired generation for foreseeable future
Coal-fired electrical generation was 35% thermally efficient in 2005 (EPA)
Line-losses and battery/e-motor efficiency aren’t 0%
Therefore from a GHG perspective -TNSTAAFL
USA Energy Consumption (%) 1960
1970
1980
1990
2000
Oil 44.1 43.5 43.6 39.8 38.5
Natural Gas 27.5 32.1 26.0 22.9 23.7
Coal 21.8 18.1 19.6 22.8 22.7
Nuclear Energy .002 0.35 3.5 7.3 8.1
Hydro-,Geothermal,Solar, Wind,etc
6.6 6.0 7.2 7.4 6.9USA Electricity Generation (%)
1990
2000
Coal 52.6 51.8
Petroleum 4.1 2.9
Natural Gas 12.5 15.7
Nuclear 19.1 19.9
Hydroelectric 9.7 7.2
Geothermal 0.5 0.4
Wood 1.0 1.0
Waste 0.4 0.6
Other Waste 0.076
.09
Wind 0.099
0.129
Solar 0.020
0.021
4419 April 08
Transportation Effects on GHG - Future
4519 April 08
4619 April 08
By 2020,
1.1 billion vehicles (an increase of 300 million) will circle the earth 125 times.
Energy diversity is required in the future. Reducing dependence on petroleum is imperative.
4719 April 08
“At GM, we believe tomorrow’s automobiles must be flexible
enough to accommodate many different energy sources.”
“At GM, we believe tomorrow’s automobiles must be flexible
enough to accommodate many different energy sources.”
- Rick WagonerChairman and CEOGeneral Motors CorporationLA Auto Show 11/29/2006
“ And a key part of that flexibility will be enabled by the development
of electrically driven cars.”
4819 April 08
Hybrid, Electric & Fuel Cell Vehicles Introduction & Background – More definitions
Vehicle TypeElectric Power
Onboard Electric Storage
Grid ConnectedRecharging?
Electric- only Driving
Mild HEV low low no no
Full HEV med low no limited
PHEV med med yes limited
E-REV high high yes Full
Ele
ctr
ificati
on
4919 April 08
1st & 2nd Generation Biofuels
Transportation Challenge – Energy Diversity - Source Blending via Electrification
Energy Resource Energy Carrier Propulsion System Conversion
BiomassBiomass
CoalCoal
Natural GasNatural Gas
Renewables (Solar, Wind, Hydro)Renewables
(Solar, Wind, Hydro)
NuclearNuclear
Energy Resource Conversion Energy CarrierPropulsion System
Conventional ICE:Gasoline/Diesel
Conventional ICE:Gasoline/Diesel
Mild and Full Hybrids
Mild and Full Hybrids
Plug-In Hybrid
Plug-In Hybrid
Battery Electric Vehicle
Battery Electric Vehicle
FC Electric VehicleFC Electric Vehicle
Thermochemical
Water-Splitting
Oil(Conventional)Oil(Conventional)
OilOil (Non-Conventiona
l)
(Non-Conventiona
l)
Petroleum Fuels
SyngasCO, H2
FischerTropsc
hCCGT
ShiftReactio
n
LiquidFuels
Hydrogen
Electrolysis
CO2 Sequestration
Extended Range EV
Batt
ery
Energ
y S
tora
ge
Batt
ery
Energ
y S
tora
ge
Electricity
More
Ele
ctri
fica
tion
5019 April 08
Transportation Challenge – Energy Diversity - Source Blending via Electrification
5119 April 08
Advanced Technology and Sustainability… GM Technology StrategyAdvanced Technology and Sustainability… GM Technology Strategy
5219 April 08
Chevrolet VOLT Concepts Illustrate E-REV and FC Commonality
5319 April 08
Chevrolet VOLT E-REV Concept
• Global Compact Vehicle Based
• Electric Drive Motor• 120 kW peak power
• 320 Nm peak torque
• Li Ion Battery Pack• 136 kW peak power
• 16 kWh energy content
• Home plug in charging
• Generator• 53 kW peak power
5419 April 08
E-Flex Fuel Cell Variant
• Global Compact Vehicle Based
• Electric Drive Motor• 120 kW peak power
• 320 Nm peak torque
• Fuel Cell Propulsion System
• Smaller Li Ion battery pack
• Hydrogen storage
5519 April 08
www.gm.com/corporate/careers/