Impact of Alternative Liquid Fuels on Highly Dilute Engines, 03-R8005Printer Friendly Version
Inclusive Dates: 12/01/08 04/01/09
Background - A dilute spark-ignited engine concept has been developed by Southwest Research Institute (SwRI) as a potential low-cost competitor to diesel engines. The technologies contained in the concept have enabled diesel-like efficiency and torque for light-duty and medium-duty applications with a variety of engine architectures. This has been accomplished with conventional stoichiometric, spark-ignited engine aftertreatment (three-way catalyst) eliminating the need for costly and complicated NOx and particulate matter (PM) aftertreatment systems. With advancements in ignition and flame propagation, high levels of recirculated exhaust gas (EGR) have been realized with significant benefits in emissions, efficiency, and torque. This investigation was performed to identify the potential of a light-duty (LD), dilute, spark-ignited (SI) engine to meet U.S. Tier II Bin II emissions standards. A secondary task was to evaluate the impact alcohol fuels may have on the Tier II Bin II emissions target. The primary alcohol fuel used in the US is E85 (15 percent gasoline 85 percent ethanol). The interest in using butanol has also increased as a research topic for both compression and spark-ignited engines both as a neat fuel and as an oxygenated additive. These two fuels were chosen for this investigation along with conventional gasoline. The program intended to show that utilizing EGR as an enabling technology for high efficiency does not preclude the ability to meet the most stringent emissions standards on a variety of liquid fuels.
Approach - The test engine was a four-cylinder Chrysler 2.4 L World Engine. For these experiments the engine was turbocharged, the compression ratio was increased from 10.5:1 to 11.4:1, an external low pressure loop EGR circuit was added, a prototype high energy quasi-continuous spark ignition system was used, and the stock spark plugs were replaced with fine center electrode iridium plugs with a gap of approximately 1.65 mm. Modification to the stock head and piston were made to improve dilution tolerance. A research class engine controller, developed at SwRI, was used for air-fuel ratio (AFR), EGR, spark, and valve timing control. The fuels used in this investigation were Haltermann EEE (HEEE) pump grade E85 and normal butanol (n-butanol). A Horiba 5 gas exhaust analyzer was used to measure carbon dioxide (CO2), carbon monoxide (CO), oxygen (O2), total hydrocarbons (THC), nitric oxide and nitrogen dioxide (NOx) in undiluted engine exhaust. Other gaseous compounds including formaldehyde and acetaldehyde were measured with a Fourier Transform Infrared Spectrometer (FTIR). Particulate matter was measured in two ways. Mass was measured with a "partial dilution / partial sample" based on EPA part 86 and used Whatman PP47 filters. Particle count and size were measured with an Engine Exhaust Particle Sizer (EEPS™) spectrometer.
Accomplishments - The work found that EGR can moderately reduce PM at mid to high speeds and loads, and significantly reduced PM when compared to conditions where fuel enrichment is required for a non-EGR engine. Drive cycle simulations indicate PM aftertreatment will not be necessary to meet the Bin II target. EGR was found to moderately increase formaldehyde emissions, but should be controllable with a three-way catalyst. E85 and butanol were found to moderately decrease PM, but significantly increase formaldehyde. Assuming good EGR system durability and control, the primary concern for a spark-ignited, port fuel-injected, EGR dilute engine to meet Bin II certifications will be the formaldehyde standard.