No abstract

Because of the large discharge of marine diesel engines, direct measurement is difficult and complicated. In order to obtain accurate data of marine diesel engine exhaust flow, the carbon balance method is generally used for calculation, but the carbon balance method has iterative operation, adopts wet concentration calculation, and does not consider sulfur oxide components, thus resulting in errors in the calculation results. In this paper, according to the calculation model of air-fuel ratio proposed by S H Chan, the law of conservation of C, H, and O atoms is observed, sulfur oxides in the exhaust are considered, and a new exhaust flow calculation model based on air-fuel ratio is obtained. This calculation model is the first to directly use dry gas concentration in the calculation model of air-fuel ratio. Then, the simplified calculation model is obtained by ignoring CO and simplifying coefficient A ∗ , the difference between the carbon balance method, ignoring CO, and the simplified model is compared, and then the exhaust flow value and exhaust density are calculated by the test data. The simplified calculation model can also calculate the mass flow rate of carbon dioxide, unburned hydrocarbon, and carbon monoxide. Finally, a software program is developed for the simplified calculation model, which is convenient for quick calculation and quick acquisition of exhaust flow data, thus laying a solid foundation for the application of the simplified calculation model in real ships.

Natural gas/diesel dual-fuel engine has become an urgent need to alleviate the energy crisis and reduce emissions. As an additive, reforming gas can improve the combustion process of dual-fuel engines because it improves the combustion rate and compensates for the low reactivity of natural gas. Therefore, it is of great significance to study the ignition characteristics of natural gas diesel blends by adding H2 and syngas. Based on ANSYS Chemkin 17.0 software, the ignition delay time was solved by a closed uniform model. The effects of H2 and syngas on the ignition performance of a natural gas/diesel engine were studied. The results showed that the ignition delay time of the methane/n-heptane mixture was prolonged after adding H2 in the range of medium and low temperatures. This was due to the fact that reaction R3 (OH + H2 = H + H2O) was an endothermic reaction, which consumed OH radicals and inhibited the ignition process. In the high-temperature range, adding H2 reduced the ignition delay time of the mixture system, which was because of the significant increase in the sensitivity coefficients of R1(H + O2 = O + OH) and R3 and the generation of OH radicals. Therefore, the reduction in ignition delay caused by H2 addition in the high-temperature regions was mainly attributed to R3 and R1. In syngas, CO reduced the ignition delay time of methane/syngas/n-heptane. However, the addition of CO could reduce the importance of R3 in the reaction process—resulting in the weakening of the influence of H2 on ignition delay. This study can expand the theoretical basis of ignition characteristics of methane/n-heptane mixture with H2 and syngas under dual-fuel engine-relevant conditions.

Among existing diesel engines, fuel improvement through additives is an attractive option to meet increasingly stringent pollutant emission regulations for diesel engines. Because of the good REDOX properties of rare earth materials, it can improve the combustion performance of diesel engines and reduce pollutant emissions. This paper characterizes the performance of inorganic acid rare earth and organic acid rare earth and analyzes the emission reduction performance from the crystal structure, which aim to compare the effects of inorganic acid rare earth and organic acid rare earth on the emission reduction performance of existing diesel engines under similar conditions. The emission reduction performance of two rare earth fuel additives of cerium carbonate and cerium stearate in Changchai twin-cylinder direct injection diesel engine at five rotational speeds is contrastively studied. The experimental results show that two kinds of rare earth fuel additives can effectively reduce NO X , CO and HC emissions of diesel engines. And the maximum reduction rate of NO X , CO and HC in cerium carbonate is 11.37%, 14.63% and 13.80% respectively, while the maximum reduction rate of NO X , CO and HC in cerium stearate is 10.19%, 12.15% and 9.40% respectively. Cerium stearate has higher NO X , CO, HC and PM emissions than cerium carbonate due to its small specific surface area. So the emission reduction effect of cerium carbonate is better than that of cerium stearate.

As fuel additives, lanthanum and cerium are the most active rare earth elements. In order to compare the emission reduction performance of the two rare earth elements additives, lanthanum oxalate and cerium oxalate are used as the comparison objects in this paper. In order to reduce the error, it is necessary to prepare lanthanum oxalate and cerium oxalate. After lanthanum oxalate and cerium oxalate was prepared by precipitation method, a series of modern characterization methods, such as XRD, SEM, EDS and BET, are used to characterize and analyze the self-made additive powder, and the relationship between the emission reduction performance and the internal relationship is analyzed. By changing the ratio of fuel additives and carrying out the emission test on the self-built diesel engine platform, the optimal amount of additives is obtained. Fuel additives of lanthanum oxalate and cerium oxalate with a mass fraction of about 45mg/L for diesel engine is a more suitable choice. Cerium oxalate has better emission reduction performance than lanthanum oxalate. The conclusion is that reasonable use of two organic acid rare earth fuel additives can greatly reduce NO X , CO and hC emissions from diesel engines.