Natural Gas as a Transportation Fuel

Sohail GhanchiEnergy Technology and Policy

The University of Texas at Austin

Overview

IntroductionBenefitsAvailable TechnologiesCurrent UsesImplementation ChallengesConclusion

What is Natural Gas?

A combustible gaseous mixture of hydrocarbons, primarily methane

Primarily extracted from oil and gas wells. Large deposits exist in 25 states

Accounts for 22% of US energy use and 2.2% of energy used for transportation

Benefits

Increased Energy Security Natural gas is a domestically available fuel

Public Health and Environment Protection Up t0 95% less particulate matter (compared to

diesel) 21-25% less greenhouse gas emissions*

CNG vs. LNG

CNG – 116,000 vehicles Most common method of storing natural gas Typical pressures range between 2,000 and

4000 psi (household NG pipe pressure is ~1-2 psi)

LNG – 3000 vehicles Natural gas liquefies at -260F LNG tanks are much more expensive than

CNG tanks Can store a lot more NG, but must be kept

cool at all timesSource: DOE

NG Engine Technology

Stoichiometric Natural Gas Engines Operates with air/fuel mixture that contains only enough

oxygen to burn all the fuel Used in majority of light duty NG vehicles because they

require low power Lean Burn Technology

Far more air than needed to burn the fuel Lowers peak combustion temp lower NOx and PM

emissions Used in trucks and buses

Closed Loop Fuel Control

NG Fuel Quality

If standards are not met, air-fuel ratio in engine is disturbed, causing higher emissions and a reduction in efficiency

Water – formation of ice and particulates at low temperatures, can plug fuel lines

Sulfur – must be minimized to maximize the emission benefitsProposed Minimum Fuel Quality

Standards

Methane 95% minimum

Propane 2-5% maximum

Butane 1-5% maximum

Sulfur 8-30 ppm maximum

Light Duty NGV

Light Duty NGV use CNG Currently limited to the Honda Civic

190-225 miles on one tank EPA certified conversions available

from a variety of companies Home refueling devices

Up to 16 hours to refill an empty tank at home

Retrofits

Gasoline to Natural Gas No significant reduction in particulate

matter emissions NOx, VOC and CO decrease if proper fuel

control and exhaust catalyst systems are installed

Diesel to Natural Gas Up to 95% reduction in particulate

matter emissions

Heavy Duty NGV

May use LNG or CNG Larger engines typically use LNG Natural Gas Transit buses – largest niche

NG market Annual consumption (2006): 109 million

diesel gallon equivalent of natural gas 15% of transit vehicles in 2006 powered

by natural gas

Implementation Challenges

Vehicle Price – Natural gas vehicles cost more because of onboard fuel storage and engine modifications

Fuel Availability – Refueling is less readily available outside of California - most fleets build their own infrastructure

Natural Gas Fueling Stations

More than 825 natural gas fueling stations in the United States:

• 35 LNG• 790 CNG• 355 Public• 470 Private

Source: DOE AFDC, Feb 2008

Tax Incentives

Vehicle Tax Credits (for new or retrofits) Light Duty (up to 8,500 lb): up to $5,000 Medium Duty (up to 14,000 lb): up to

$10,000 Medium-Heavy Duty (up to 26,000 lb):

up to $25,000 Heavy Duty (more than 26,000 lb): up

to $40,000

Conclusions

Fuel quality must be controlled to allow for clean and durable vehicle operation

Increased production of NGVs will stimulate the construction of fueling stations

Heavy duty vehicles are best suited for NG usage