(641g) The Impact of Ethanol and Iso-Butanol Blends on Regulated Emissions, Air Toxics, and Particle Emissions from SIDI Vehicles
Spark-ignition gasoline direct injection (SIDI) vehicles have been the subject of several studies, with much of this work has been done outside the U.S., as this is where GDI vehicles have been more prominent. The penetration of SIDI vehicles in the U.S. market is rapidly growing with most domestic automotive manufacturers offering direct injection versions in their existing models. The SIDI technology has emerged from the need to improve the thermodynamic efficiency (and thus reduce fuel consumption) and power output of spark ignited engines. The improved fuel efficiency compared to the conventional port fuel injection (PFI) vehicles could potentially provide the manufacturers the means to meet the target set in the U.S. on the fleet-average carbon dioxide (CO2) emissions of future vehicles. It is foreseen that this category of vehicles will dominate the gasoline market, eventually replacing the conventional and less efficient PFI vehicles. However, SIDI engines are known to emit more particulate matter (PM) emissions than homogeneous-charge PFI spark-ignited gasoline engines and diesel engines equipped with diesel particle filters (DPFs) in the exhaust system. In particular, it is likely that SIDI vehicles will be higher than 3 mg/mile CARB LEVIII PM Standard through 2021, whereas PFI vehicles generally emit below 1 mg/mile, and often below 0.5 mg/mile, providing the potential to more than double PM emissions from new light-duty vehicles. The PM characteristics of direct injected spark ignition engines in comparison to conventional PFI engines can be mainly attributed to the injection characteristics. There is a growing consensus amongst the health experts that particles in the ultrafine range (smaller than 100 nm) are potentially more toxic and have greatest adverse health effects on human health.
Limited studies have investigated the influence of alternative fuels on the exhaust emissions, especially particulate emissions, from SIDI vehicles. The fuels employed in these studies were mainly low and mid-level ethanol blends. Currently, ethanol is the most widely used renewable fuel for transportation in the U.S. and with the push to use increasingly higher levels of renewable fuels, there has been an accompanying push to further increase the ethanol level in gasoline. The EPA Renewable Fuel Standard version 2 (EPA-RFS2) and the California Low Carbon Fuel Standard (CA-LCFS) are driving the U.S. market for the development of biofuels. The EPA-RFS2 requires that 36 billion gallons of renewable fuel are available in the U.S. market by 2022, with ethanol expected to make up the majority of this requirement.
Another pathway that could be used to reach the congressionally mandated biofuel volumes is the use of bio-butanol. Analogous to ethanol, butanol can be produced both by petrochemical and fermentative processes. Biomass-derived butanol can be produced by alcoholic fermentation of biomass and agricultural feedstocks, such as corn, wheat, sugar beet, sugarcane, etc. Butanol offers a number of advantages over ethanol for transportation use. Butanol has considerably higher energy content than ethanol. Butanol is less hydroscopic and less corrosive than ethanol, therefore, it is more suitable for distribution through pipelines, whereas ethanol must be transported via rail or truck. Moreover, in blends with gasoline, butanol is less likely to separate from the base fuel than ethanol if the fuel is contaminated with water. Butanol has a lower vapor pressure and a higher flash point than ethanol. The heat of vaporization of butanol is also less than half of that of ethanol.
The literature is particularly poor with respect to studies on butanol/gasoline blends on SIDI engines. In addition the effect of oxygenated fuels especially on particulate emissions from SIDI engines is not well understood. The purpose of this investigation is to elucidate the effects of fuel type and blend concentration for ethanol and iso-butanol on the exhaust emissions from two different modern technology stoichiometric SIDI wall-guided light-duty vehicles fitted with three-way catalysts (TWC). The vehicles were tested over the Federal Test Procedure (FTP) and the Unified Cycle (UC) on light-duty chassis dynamometer. The fuel blends included E10, E15, E20, Bu16, and a E10/Bu8 blend. A total of seven fuels were employed in this study, including an E10 fuel, which served as the baseline fuel, and two more ethanol blends, namely E15 and E20. For this study, iso-butanol isomer was blended with gasoline at proportions of 16, 24, and 32% by volumes, which are the E10, E15, and E20, respectively, equivalent based on the oxygen content. The seventh fuel was an alcohol mixture consisting of 10% ethanol and 8% iso-butanol. This mixed alcohol formulation was equivalent to E15 based on the oxygen content. Each vehicle was tested on each fuel over three FTP and three UC tests. Measurements of regulated emissions were made for nitrogen oxides (NOx), carbon monoxide (CO), total hydrocarbons (THC), nonmethane hydrocarbons (NMHC), methane (CH4), and CO2. Special attention was paid to gaseous air toxics, including carbonyl compounds (aldehydes and ketones) and volatile light aromatic hydrocarbons (benzene, toluene, ethylbenzene, and xylenes), and 1,3-butadiene. Particle emissions were characterized by defining PM mass, total particle number, particle size distributions, and black carbon concentrations. The results of this study will enhance our understanding of alcohol fuel formulations effects on gaseous and particle emissions from emerging vehicle technology.