An innovative alternative fuel system that is composed of acetylene as primary fuel and alcohol (or other high-octane fuel) as secondary fuel has been developed for use in an internal combustion engine. The system was described by J. Wulff et al. at the American Institute of Chemical Engineers Annual Meeting held November 12-17, in Los Angeles, California.
Increasingly stringent specifications on exhaust emissions from internal combustion engines powered by gasoline and diesel have encouraged substantial research on clean-burning alternative fuels. Dual-fuel systems that burn cleanly and with high efficiency are of interest in this area. An alternative fuel that has not been investigated in depth for this purpose until now is acetylene. According to Wulff et al., acetylene can be effectively utilized in both on-road and off-road applications.
Acetylene is conventionally produced by reacting calcium carbide with water. The reaction is spontaneous and can be conducted without any sophisticated equipment or apparatus. The clean burning nature of acetylene is self-evident from the combustion equation:
C2H2 + 2.5O2 = 2CO2 + H2O
The reaction proceeds spontaneously at any temperature and pressure conditions and readily goes to completion forming carbon dioxide and water, thus leaving no residue of carbon or carbonaceous matter. Further, the reaction ideally takes place in the gaseous phase without any need for a catalyst.
On the other hand, gas-phase reactions involve different measures, controls and safety precautions. If acetylene is used either in pure form or in concentrated form, there is a strong tendency for detonation, which directly contributes to undesirable spontaneous chemical reactions in internal combustion engines, often called "knocking." Thus, acetylene as a single fuel cannot be burned in an internal combustion engine of conventional design without severe knock and early ignition in the intake port and in the cylinder, causing severe engine damage. This knocking can be totally eliminated, say Wulff et al., by addition of a secondary fuel element, whose portion in the total fuel based on the BTU output is typically less than 10 percent.
The alternative fuel system they describe comprises a dual-fuel engine having a primary fuel and a secondary fuel. The primary fuel is pure acetylene or a mixture of acetylene (as a principal ingredient) and one or more fluids (as a minority ingredient) such as alcohols, ethers and low-molecular weight esters. The secondary fuel is comprised of suitable alcohols, ethers, esters, or other combustible fluids. Start-up and operation of an internal combustion engine utilizing the dual fuel generally comprises two stages. The first stage involves starting the engine with the secondary fuel and, after a relatively short warm-up period, the second stage involves generating power output by the engine, largely through combustion of the primary fuel. Injection of the secondary fuel serves to accomplish early ignition and prevent knocking.
Emission testing on small internal combustion engines with this alternative fuel system was conducted by Shell Engineering and Associates Inc. The fuel and engine testing experiments were performed on an 8.0-horsepower gasoline-fired engine and a 9.0-horsepower diesel-fired engine. The alternative fuel tested on the gasoline engine was an acetylene-based dual fuel. Methanol was the secondary fuel. The NOx, CO and volatile organic compound exhaust emissions were lower than the values of the United States Environmental Protection Agency’s (EPA) AP-42 emission standards by 85.7, 91.6 and 96.3 percent, respectively. Considering the tested engine was not equipped with any catalytic converter, this emission result exceeds the estimated future standards for year 2008.
The diesel engine was started at idle on diesel fuel and switched to the alternative triple fuel which was acetylene with 5 percent methanol and 5 percent diesel. The NOx and CO exhaust emissions were lower by 87.6 and 40.4 percent, respectively, than the EPA’s AP-42 emission standards. Substituting ethanol for methanol and soy diesel for diesel produced similar exhaust emission results.
This study proved that gasoline and diesel engines can run effectively on an acetylene gas/alcohol mixture. The small amount of alcohol retarded the knock and reduced the engine temperature in both engines. The dual alternative fuel of acetylene and alcohol, demonstrated large reductions in nitrogen oxides, carbon monoxide and volatile organic compounds in comparison with the conventional fuel, on both gasoline and diesel engines. Opacity was not observed from the exhaust pipe.
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