Reduction of soot and NOx emissions from a prechamber-type diesel engine is studied by employing both chemical and physical aspects of the fuel and induction method. Fuel modification was performed to produce several forms of composite fuel: solution of alcohol and gas oil (JIS No. 1); emulsification and mixture of methyl alcohol-gas oil prepared by off- and in-line fuel systems; and separate injection of fuels into the pre- and main-chamber.
Those composite fuels were introduced by using both conventional and unconventional fuel induction methods to have the following cases of engine experiment: (1) injection of alcohol-gas oil solution into the pre-chamber; (2) injection of stabilized emulsified fuels into the pre-chamber; (3) timed injection of gas oil and methanol into the prechamber to have them in-line mixing by using a newly designed hydroshear device: (4) controlled sequential injection of gas oil and methanol into the pre-chamber through a new adaptor device; and (5) separate injection of gas oil into the pre-chamber and methanol into the main-chamber.
In all the cases of composite fuels and induction (chemical and physical) methods investigated in the present study, the brake thermal efficiency (BTE) increased with the portion of alcohol in the composite fuel (R), and peaked when R=15% in volume. When R=30%, the BTE, however, was comparable with measurements from the operation by neat gas oil (i.e., baseline data). Thereafter, it decreased somewhat with increase in R, that is, by about 10% when R=50%. The increase of BTE in case-(3) for the entire range of R studied, was most encouraging.
Comparing the emission data obtained from operation at R=50% with the baseline measurements, cases-(1) and -(2) produced emissions of soot and NOx lower by 30-50%; case-(3) resulted in the emissions lower by over 50%; case-(4) emitted them lower by about 30%; and case-(5) had the emissions lower by about 20%. Note that although the emissions of unreacted hydrocarbon and formaldehyde at R=50% were a bit higher than the baseline measurements, they were still negligibly low in absolute values.
It is especially noted that the timed injection of gas oil and methanol using the new hydroshear device produced highly promising results in both BTE and emissions. Some probable reasons for the results were considered in terms of modifications in both chemical and physical aspects of this composite fuel method.