Transient Cycle Emissions Testing
for Heavy-Duty Diesel, Gasoline, and Alternative Fuel Engines
Transient Emissions Programs
For more than 15 years, Southwest Research Institute (SwRI) has characterized heavy-duty engine emissions using the Environmental Protection Agency (EPA) transient test, steady-state tests, and the European ECE-49 and ISO 8178 procedures.
The Institute helped EPA develop and refine the transient test procedure and helped produce the initial baseline study. Subsequently, the Institute has provided domestic, European, Japanese, and other engine manufacturers with certification assistance, engine and emission control development, and determination of deterioration factors.
Ten transient test cells have heavy-duty (HD) diesel capability, four are equipped to test HD gasoline engines, and four have alternative fuel (alcohol, natural gas, and LPG) capability. Additional diesel and multiple-fuel transient testing facilities are under development. Engine break-in and durability test facilities are also available to maximize program efficiency.
SwRI capabilities include:
The EPA defines particulate as all material collected on a fluorocarbon-coated glass fiber filter at or below 125 degrees F. SwRI weighs filters before and after the transient test to assess particulate emissions. Condensed water is excluded by using exhaust dilution techniques. Temperature- and humidity-controlled weighing chambers with sensitive balances determine weight gain of test filters to assess particulate mass emissions.
Because most HD studies require particulate emission measurement, SwRI developed the capability to obtain several particulate samples simultaneously. Double-dilution techniques, coupled with special filter holders, provide representative diesel particulate samples for characterization. Extraction of soluble organic fraction (SOF) and subsequent analysis for Ames bio-assay, nitroaromatics, and polynuclear aromatics can be performed on auxiliary particulate samples. Using the Tapered Element Oscillating Microbalance (TEOM), SwRI identifies and explores, in real time, contributors to total particulate emissions.
Unregulated Emissions Measurements
During transient tests, SwRI focuses on acquiring representative samples of engine exhaust. Although regulated emissions of total hydrocarbons, carbon monoxide, oxides of nitrogen, total particulate, and smoke opacity are of prime concern, representative emission samples are analyzed for a variety of other compounds.
Using analytical techniques, SwRI determines levels of aldehydes, sulfates, benzene, unburned alcohols, B(a)P, 1,3-butadiene, speciated hydrocarbons, methane, and other unregulated emissions.
To control total particulate, SOF is of special interest to engine manufacturers and regulatory groups. SwRI not only determines SOF by conventional solvent extraction techniques but has established a direct filter injection gas chromatography (DFI/GC) technique that eliminates the need for expensive and sensitivity-limiting solvent extractions.
Specialized Transient Emissions Testing
With broad transient emission measurement capabilities, SwRI provides engine manufacturers, regulatory agencies, and others the ability to explore the spectrum of emission control technology. With programs in catalytic aftertreatment, production engine emissions surveillance, vehicle testing, and high-altitude simulation, the Institute develops a variety of effective emissions control strategies.
During production, engine manufacturers must determine that engines meet emissions expectations. SwRI conducts a variety of surveillance programs, providing transient emissions information that fulfills corporate and regulatory requirements. The Institute also provides the cyclic or special break-in operations diesel and gasoline engines often require prior to emissions testing.
The Institute provides constant volume sampling for transient emissions at normal atmospheric conditions and explores regulated and unregulated transient emissions of diesel engines at various altitudes. SwRI's special exhaust dilution system samples diesel engine exhaust over the transient cycle while simulating altitudes to 10,000 feet.
Aftertreatment technology becomes increasingly important as
engine manufacturers seek to decrease emissions and improve performance and durability.
The Institute investigates various concepts and materials helping manufacturers develop
advanced particulate traps. Using transient and special-cycle tests, SwRI examines various
catalytic strategies used to control diesel, gasoline, and alternate fuel emissions.
Trucks and buses are operated on SwRI's special chassis dynamometer for a range of applications. A large dilution tunnel sampling system accommodates transient emission tests for vehicles to 84,000 pounds GVWR. Using this system, SwRI studies driveability and emissions using conventional or alternative fuels and hybrid systems.
Transient Federal Testing
Early HD engine emissions characterizations were limited to steady-state operating conditions. Improvements in sampling strategy and dynamometer controls now allow exploration of emissions under transient operating conditions. Since 1984, the EPA has required transient emissions certification testing of all HD on-road engines sold in the U.S. The transient Federal Test Procedure (FTP) outlines specifications and procedures for transient emissions testing for regulatory purposes.
The FTP includes requirements for test engine setup and for mapping full-torque capabilities over an engine's operating speed range. Engine-specific performance data are used, along with a normalized EPA transient cycle, to define a transient command cycle for test engine operation. The 20-minute transient command cycle shown below depicts the rapid speed and torque changes an engine must produce.
During the 20-minute test cycle, engine torque and speed responses are compared to the command cycle to ensure FTP compliance. Simultaneously, engine exhaust gases are diluted with conditioned air, and relevant emissions are determined. The measured emissions are divided by the total work performed during the test, and HD engine emissions are reported in terms of pollutant mass per unit of work.