Mitigation of Emissions through Injection Strategies for C I Engine

Fuel conversion efficiency is high with diesel engines compared to petrol engines. However high emissions from diesel is a matter of concern and its mitigation paves way for scope of research. Exhaust gas recirculation is one of the method widely accepted to curb NOx emissions. Recently, split or multiple-injection strategy has been explored by researchers to precisely control the fuel injected per cycle and also to mitigate emissions. Present work reflects technical review of effect of injection strategies on performance, emissions and combustion on C.I. engine with diesel and biodiesel as fuel. Injection strategies like duration of injection, number of injections, the dwell period between two injections, quantity of injection, and multiple injections are analyzed for their influence on engine output and brake specific fuel consumption. Also their effect on emissions especially soot and NOx emission are reviewed. First the effect of injection strategies with diesel fuel is discussed followed by biodiesel.

Modeling of diesel spray tip penetration during start-of-injection transients

Multiple-injection strategy that has been applied widely in diesel engines usually features a short duration for each injection pulse. As a result, the shortened injection makes the needle opening and closing transients increasingly important for spray in an injection event. Owing to the needle movement, the spray development during the transient processes is complex and quite different from the spray at the quasi-steady state. However, so far modeling of the spray development during the transient processes is far from adequate. Particularly, a theoretical zero-dimensional (0-D) spray tip penetration model considering the needle opening and sac pressurization processes as well as ambient and injection conditions during the start-of-injection (SOI) transients is still absent. In this paper, considering the sac pressurization processes, the 0-D model of spray tip penetration during the SOI transients is derived. Then, the model is validated against the experimental spray data using a long-distance microscope together with an ultrahigh speed CMOS camera. The model and experimental results show that the spray tip penetration shows a t3/2 dependence at the initial stage of injection rather than the t dependence suggested by Hiroyasu’s model. Later, the spray tip penetration shows a t3/4 dependence owing to the spray breakup, and a t1/2 dependence with the completion of sac pressurization. The models and analysis are believed to provide new insights into the transient spray behaviors and valuable reference for engineers and researchers who are considering the model-based development of next-generation diesel engines.

Analysis of the Influence of Diesel Spray Injection on the Ignition and Soot Formation in Multiple Injection Strategy

Multiple injection strategies have increased their capabilities along with the evolution of injection system technologies up to the point that nowadays it is possible to inject eight different pulses, permitting to improve the engine performance, and consequently, emissions. The present work was realized for two simplified strategies: a pilot-main and a main-post, in order to analyze the influence of an auxiliary pulse on the main and otherwise, in reactive conditions for two pilot/post quantities and four hydraulic dwell times. The study was carried out by employing two optical techniques: diffused back-illumination with flame bandpass chemiluminescence for measuring soot, represented by soot-maps distribution, and single-pass schlieren for ignition delay (ID). Furthermore, a novel methodology for decoupling the start of combustion (SOC) of the second pulse was developed and successfully validated. From the ignition delay results, it was found for all test points that the pilot injection enhanced conditions, which promote a faster ignition of the main pulse, also at higher chamber temperatures, all conditions presented a separate combustion event for each injection. In emission terms, soot increased in the pilot-main strategies compared to its single injection case, as well as, in conditions that promote faster-premixed combustion.