Mechanism of Methane Addition Affects the Ignition Process of n-heptane under Dual Fuel Engine-Like Conditions

For saving energy and protecting the environment,natural gas has been widely used in internal combustion engines,which makes the study on the ignition characteristics of natural gas/diesel mixtures important.In this work,the effects of trace methane addition on the ignition delay of n-heptane/air mixtures are numerically studied using a detailed n-heptane mechanism under marine engine-like conditions.The simulations are carried out based on the software CHEMKIN-PRO 18.0 with a closed homogeneous reactor.Results show that the prolonged ignition delay times(IDs)of n-heptane/air mixtures are observed over the whole initial temperature range after methane is added,and the increment of IDs in the negative temperature coefficient(NTC)region is significantly higher than that in high temperature region.The sensitivity analysis indicates that both inhibition and promotion effects of important elementary reactions on n-heptane oxidation are weakened because of methane addition.However,the weakening influence on the promoting effect is more prominent.In addition,the inhibition effect of some elementary reactions that are related to the methane oxidation is enhanced.Thus,the IDs of n-heptane/air mixture are prolonged.The analyses of reaction rate of production(ROP)show that the both the production and consumption rates of key radicals decrease significantly in NTC region after methane is added,but it is negligible in the high temperature region.The study can extend the theoretical basis of ignition characteristics of methane/n-heptane blends under elevated temperatures and pressures.

Effect of the chlortetracycline addition method on methane production from the anaerobic digestion of swine wastewater

Effects of antibiotic residues on methane production in anaerobic digestion are commonly studied using the following two antibiotic addition methods：（1） adding manure from animals that consume a diet containing antibiotics, and（2） adding antibiotic-free animal manure spiked with antibiotics. This study used chlortetracycline（CTC） as a model antibiotic to examine the effects of the antibiotic addition method on methane production in anaerobic digestion under two different swine wastewater concentrations（0.55 and 0.22 mg CTC/g dry manure）. The results showed that CTC degradation rate in which manure was directly added at 0.55 mg CTC/g（HSPIKE treatment） was lower than the control values and the rest of the treatment groups. Methane production from the HSPIKEtreatment was reduced（p 〈 0.05） by 12% during the whole experimental period and 15% during the first 7 days. The treatments had no significant effect on the pH and chemical oxygen demand value of the digesters, and the total nitrogen of the0.55 mg CTC/kg manure collected from mediated swine was significantly higher than the other values. Therefore, different methane production under different antibiotic addition methods might be explained by the microbial activity and the concentrations of antibiotic intermediate products and metabolites. Because the primary entry route of veterinary antibiotics into an anaerobic digester is by contaminated animal manure, the most appropriate method for studying antibiotic residue effects on methane production may be using manure from animals that are given a particular antibiotic, rather than adding the antibiotic directly to the anaerobic digester.