Estimates of the air-fuel ratio at the time of ignition in a pre-chamber using a narrow throat geometry

The benefits of pre-chamber combustion (PCC), such as improved engine efficiency and reduced NOx emissions, are primarily observed when operating at lean conditions with an active pre-chamber, where auxiliary fuel is supplied directly to the pre-chamber. Estimating the pre-chamber excess air ratio (λ) is important in the active pre-chamber concept to gain insights into the pre-chamber combustion phenomenon. Experimental investigations were performed using a narrow-throat pre-chamber at global-λ 1.6, 1.8, and 2.0. The fraction of fuel energy injected in the pre-chamber over the total fuel energy was fixed at 3%, 7%, and 13% for each global-λ. The mixture formation process inside the pre-chamber is first simulated using the 1-D simulation software GT-Power to analyze the pre-chamber λ at the ignition timing. However, the 1-D results were unable to reproduce the experimental observations on the pre-chamber pressure buildup accurately. Upon simulating the same conditions using the 3-D CFD software CONVERGE, the pre-chamber λ estimated from the CFD model is well-correlated to the experimental data. The CFD results indicate that the amount of fuel trapped in the pre-chamber at the inlet valve closing timing is over-predicted by the 1-D simulations. A correlation between the injected and the trapped fuel in the pre-chamber is proposed by theoretical scavenging models and applied to the 1-D simulation results to improve pre-chamber λ prediction accuracy.

Assessment of the impact of the technical condition of the cylinder-piston group parts on nitrogen oxide emissions

Nowadays, a lot is paid to environmental protection issues, including those related to reducing emissions from ships of the sea and river fleet, which is reflected in many works. Constant control over the content of harmful emissions in the environment forces us to deal with the issues of reducing emissions from diesel engines at the design stages and during operation. The solution to this problem allows us to consider 2 directions: constructional and the use of special equipment for capture and neutralization. In the best case, a combined method can be used, i.e. constructional with the use of capturing equipment for harmful components in diesel exhaust gases. This paper presents an analysis of the influence of various factors that reduce the load on the atmospheric air from nitrogen oxides of marine diesel engines, namely, from the operating settings of the diesel engine and its wear. On the ships of the river fleet, diesel engines are used with various mixture formation with volumetric, volumetric-film, vortex mixture formation. The leader in the listed group is the volumetric mixture engines. The paper provides an assessment of the research carried out to analyze various methods of influencing the working process of a diesel engine - the type of mixture formation, wear of the cylinder sleeve in order to determine their influence on the formation of NOx emissions.

Determining basic characteristics of stabilizer micro torch burners for the combustion of ballasted fuel gases

This paper reports an experimental study into the combustion of alternative gases in the form of a mixture of propane-butane with air and carbon dioxide after a stabilizing flat module whose both sides are flown around with an airflow. The ballasted fuel was fed by jets into the airflow from the holes located on the side walls of the stabilizer. In this case, the fuel and air were partially premixed. It was established that when ballasting fuel with inert admixtures, the length of the torch and the maximum temperature gradually decreased while nitrogen oxide emissions decreased. With an increase in the content of ballast in fuel, combustion breaks. The dependence of torch stability on the relative consumption of ballast has been established. To stabilize the combustion, highly reactive fuel is supplied to the recirculation zone after a stabilizer from a separate collector. Ballasted fuel passes through the next torches of high-temperature fuel; the all fuel combustion process takes place. The combined scheme of mixture formation makes it possible to adjust fuel consumption in the zones and thus maintain a stable burner power. In the case of supplying all fuel to the recirculation zone after the stabilizer, a so-called "rich" detachment is possible when the torch is detached from the stabilizer. When working under such modes, highly reactive fuel is supplied from the holes on the side walls of the stabilizer, which are placed closer to its detachment edges than the holes for the supply of ballasted fuel. At the same time, the jets of ballasted fuel also pass between the torches of highly reactive fuel so there is joint combustion of all fuel

Effects of dwell time of split injection on mixture formation and combustion processes of diesel spray

The effects of dwell time on the mixture formation and combustion processes of diesel spray are investigated experimentally. A commercial multihole injector with a 0.123 mm hole diameter is used to inject the fuel. The injection procedure is either a single or split injection with different dwell times, whereas the total amount of injected fuel mass is 5.0 mg per hole. Three dwell times are selected, that is, 0.12, 0.32 and 0.54 ms, with a split ratio of 7:3 based on previous findings. The vapour phase is observed, and the mixture formation pertaining to the equivalence ratio is analysed using the tracer laser absorption scattering (LAS) technique. A high-speed video camera is used to visualise the spray combustion flame luminosity, whereas a two-colour pyrometer system is used to evaluate the soot concentrations and flame temperature. An analysis of the mixture formation based on the spray evaporating condition reveals a more concentrated area of the rich mixture within a 0.32 ms dwell time. In the shortest dwell time of 0.12 ms, the equivalence ratio distribution decreases uniformly from the rich mixture region to the lean mixture region. In the case involving a shorter dwell time, a suitable position for the second injection around the boundaries of the first injection is obtained by smoothly growing the lean mixture and avoiding the large zone of the rich mixture. Therefore, the shortest dwell time is acceptable for mixture formation, considering the overall distribution of the equivalence ratios. Spray combustion analysis results show that the soot formation rate of the single injection and 0.32 ms dwell time case is high and decreases quickly, implying a rapid reduction in the high amount of soot. Consequently, 0.12 ms can be considered the optimal dwell time due to the ignition delay and relatively low soot emission afforded.