Article pubs.acs.org/EF
Potential for Reduction of Exhaust Emissions in a Common-Rail Direct-Injection Diesel Engine by Fueling with Fischer−Tropsch Diesel Fuel Synthesized from Coal Chonglin Song,* Guohong Gong, Jinou Song, Gang Lv, Xiaofeng Cao, Lidong Liu, and Yiqiang Pei State Key Laboratory of Engines, Tianjin University, Tianjin 300072, People’s Republic of China ABSTRACT: Fischer−Tropsch diesel fuel has desirable physicochemical properties, with the potential to significantly reduce diesel exhaust emissions. This paper evaluates the effects of the use of Fischer−Tropsch diesel fuel synthesized from coal (CFT) on diesel exhaust emissions. A four-cylinder common-rail direct-injection diesel engine fueled with Fischer−Tropsch diesel fuel synthesized from coal, diesel fuel, and blends of the two (15, 30, and 50% CFT by volume) was used. Tests were conducted using the European stationary cycle (ESC) and constant speed/varying load test modes. In the ESC test mode, the brake-specific regulated emissions were reduced by increasing the proportion of CFT in the fuel, achieving reductions of 3.2−33.9% for carbon monoxide, 3.6−39.3% for total unburned hydrocarbon, 0.1−11.8% for nitrogen oxides, and 1.0−25.5% for particulate matter; also, a marginal decrease in the brake-specific carbon dioxide was observed. In the constant speed/varying load test modes, the use of CFT also resulted in a general reduction of regulated emissions. The percentage reductions of carbon monoxide, total unburned hydrocarbon, and nitrogen oxide emissions at low engine speed were much lower than those observed at medium and high engine speeds, while there was no significant difference in the percentage reduction of particulate matter to be observed between the three levels of engine speed. At medium and high engine speeds, the percentage reduction of carbon monoxide showed a decreasing trend with an increasing engine load, and the percentage reduction of particulate matter at light engine loads was higher than at medium or high engine loads. In addition, the geometric mean diameter of particles exhibited a slight drop as the CFT ratio in the fuel was increased. CFT has a weak ability in reducing the total particulate count when compared to Fischer−Tropsch diesel fuels synthesized from natural gas.
1. INTRODUCTION Growing vehicle pollution and limited fossil oil reserves have triggered much interest in the use of alternative fuels, because they are thought to be an effective strategy to combat these problems. Coal-to-liquid (CTL) fuel is one such promising alternative1,2 that has received considerable attention, particularly in countries where coal reserves are abundant,3 such as the United States, Russia, and China. CTL fuel can be synthesized by either a direct or an indirect route.1,2 The typical direct way is to treat pulverized coal in a reactor with hydrogen in the presence of a catalyst to produce the desired liquid products.2,4 The indirect route is more highly developed, and the usual form of the process is to gasify coal to form a gaseous intermediate, which is mainly comprised of hydrogen and carbon monoxide, and then this intermediate gas is converted into liquid fuel by catalysis using Fischer−Tropsch (FT) technology. The indirect method has advantages in terms of impact on air-quality, production of greenhouse gases, and the nature of the supporting technological infrastructure when compared to the direct synthesis route.2 Therefore, currently, FT technology is the most popular route for manufacturing synthetic fuel on a commercial scale. Besides coal, natural gas and biomass can be also converted to diesel fuel through the FT process. Regardless of feedstock, FT diesel fuels share a number of very desirable properties, such as a low level of sulfur, a low aromatic content, and a high cetane number.5,6 Moreover, FT diesel fuels can be used in contemporary diesel engines without any modification and with a negligible or weak improvement of engine efficiency.7−11 © 2011 American Chemical Society
Studies examining emissions from FT fuels have clearly shown significant reductions in exhaust pollutants, particularly with FT diesel fuels synthesized from natural gas (GTL). Alleman et al.5 reviewed the use of GTL or GTL/conventional diesel fuel blends in a variety of light- and heavy-duty vehicles and engines. On the basis of an evaluation of a large quantity of emission data collected from engine and chassis dynamometer studies, they concluded that, in almost every case, nitrogen oxides (NOx), carbon monoxide (CO), and particulate matter (PM) emissions were reduced with GTL and the average reductions were 13% for NOx and 26% for PM compared to conventional diesel fuel. The impact of FT fuel on total unburned hydrocarbon (THC) emissions was more variable. Because of the added stage of coal gasification4 and certain technological differences in the production process,12 FT diesel fuels synthesized from coal (CFT) have significantly different physicochemical properties compared to GTL, such as fuel composition, H/C ratio, distillation temperature, and viscosity, which all play an important role in the formation of exhaust emissions. Therefore, if CFT is to be widely accepted, it is important to understand how the use of CFT affects the emission characteristics of diesel engines. Until now, emission studies of FT fuels have focused mainly on GTL, with relatively few involving CFT. For this reason, this study investigates the potential for reduction of regulated exhaust emissions in a Received: September 13, 2011 Revised: November 13, 2011 Published: November 28, 2011 530
dx.doi.org/10.1021/ef201378r | Energy Fuels 2012, 26, 530−535
Energy & Fuels
Article
common-rail direct-injection diesel engine using CFT fuel and also the effect of CFT on the particle number concentration and size distribution.
2. EXPERIMENTAL SECTION 2.1. Test Fuels. Tests were conducted using five fuel formulations. The base fuel for the preparation of CFT/DF blends was a light commercial diesel fuel (DF) without any additives, and the CFT (CFT100) was supplied by Synfuels China Co., Ltd. Blend fuels containing 15, 30, and 50% CFT by volume were labeled as CFT15, CFT30, and CFT50. Specifications of these test fuels are presented in Table 1.
Table 1. Test Fuel Specifications property
CFT100
CFT50
CFT30
CFT15
DF
>74 0.76 43.9
