Computational analysis of injection-rate shapes in a small-bore direct-injection diesel engine

Abstract

The purpose of this study is to analyse the differences in the combustion process, and pollutants formation (especially soot) due to top-hat and boot injection-rate shapes at one specific high-load point of a single-cylinder small-bore diesel engine using multidimensional engine simulations. The simulations are performed using a response interactive flamelet model with detailed chemical kinetics. A detailed chemistry-based soot model is used for the prediction of soot emissions. The heights of the first and second stages of the boot shape are varied to observe the effect of the injected fuel mass distribution. In addition, results of boot shapes are compared with a trapezoidal (top-hat) shape. A detailed analysis of soot formation and oxidation is also presented for some selected rate shapes. Through computational analysis it is shown that the boot shapes have the potential to decrease combustion-generated noise and to lower emissions at the investigated load point compared to the top-hat shape. Variations in the temporal distribution of the injected fuel mass show that a lower height of the first stage and a higher height of the second stage of the boot shape result in a relatively slower rise of heat release (lower combustion-generated noise) in the early part of combustion and enhanced soot oxidation as a result of higher spray momentum near the end of injection.

Effects of Injection Rate Shape on Performance and Emissions of a Diesel Engine Fuelled by Diesel and Biodiesel B20

“…The maximum values are reached for these shapes, because the fuel amount is rapidly injected at the end of the compression stroke compared to the other shapes. Comparable results on the peak in-cylinder pressure for diesel fuel were reported in [7,15,18,20,21,23] for biodiesel usage. The increase in thermal efficiency when using triangular shapes is also reported in [18].…”

“…Comparable results regarding the NO x emissions when using diesel fuel were reported in [9,10,12,13,15,18,21,22]. However, different results are presented in [7], where, for some increases applied at the beginning of the injection rate on certain boot shapes, the decrease of NO x emissions was registered. Figure 14 exhibits the values of Soot emissions relative to the ROI shapes.…”

“…Most of them showed that the adoption of single injection strategies with modified shapes of the rate of injection can be a very efficient method for decreasing NO x emissions at some loading conditions [6]. Also, the combustion-generated noise can be reduced if there is a lower initial injected fuel mass, thus slowing down the early rapid rise of the heat release and peak pressure rise rate [7]. In other studies, the adoption of different shapes of the rate of injection has been achieved considering split injection strategies [8][9][10].…”

Multi-objective optimizations of the boot injection strategy for reactivity controlled compression ignition engines

“…They also manifested that IRS methods become less important as start of injection (SOI) advances. The effects of the boot and trapezoidal IRS were studied by Luckhchoura et al 34 The simulation results showed the boot shape has a greater potential to reduce both emissions and noise compared to the other shapes. It was concluded that by decreasing boot pressure, soot oxidation enhances and heat release rate (HRR) becomes relatively slower in the early part of combustion.…”

Dynamic modeling of a piezoelectric fuel injector during rate shaping operation

“…4–6 An example of rate shaping is shown in Figure 1, in which the injection flow rate profile does not consist of just one or more individual pulses but instead can vary over the course of the injection event. Figure 1 shows an example of a “boot profile,” 7 including a “toe” and “shank.” During the shank, the needle is largely retracted but is “hovering” during the toe. Accurately capturing the injector behavior during the toe is challenging.…”