Abstract
The present work investigates the effect of pilot fuel properties on TF combustion using premixed methane-hydrogen-air (CH4-H2-air) mixtures ignited by a small amount of diesel pilot. Especially, we are investigating the effect of the cetane number (CN) and aromatic content (AC) on TF combustion in a single-cylinder compression ignition (CI) engine at varying charge air temperatures (Tair = 25 °C, 40 °C, 55 °C) and H2 volume fractions (MH2 = 10%, 20%, 40% and 60%) at lean premixed charge mixture conditions (equivalence ratio φ = 0.5). The novelty and main findings of the work consist of the following features: 1) besides the effect of H2 concentration and charge-air temperature, pilot fuel properties also play a crucial role in TF combustion, even a small amount of diesel pilot could dramatically affect the engine performance and combustion stability, 2) the CN and AC are the key factors affect the ignition delay time (IDT) and indicated thermal efficiency (ITE), 3) the in-cylinder pressure oscillation analysis based on a novel Superlets (SL) approach indicates that pilot fuel properties are important to the combustion states and combustion stability.
Highlights
Global warming and local pollution caused by the wide application of fossil fuels in internal combustion engines (ICEs) have been attracted many concerns in the industry and academia
Fuels with a high cetane number (CN) can shorten the ignition delay time (IDT), which leads to a premixing time for diesel pilot and charge mixture
With the increase of the Tair or MH2 (Tair ! 40 C and/or MH2!20%), the premixed mixture ignition in the end-gas region (PREMIER) combustion caused by the end-gas autoignition creates a small pressure rebounding after CA50, which is presented in aHRR, as shown in Fig. 5 (b) (Tair 1⁄4 55 C and MH2 1⁄4 20%) and Fig. 5 (c) (Tair 1⁄4 40 C and MH2 1⁄4 40%)
Summary
Global warming and local pollution caused by the wide application of fossil fuels in internal combustion engines (ICEs) have been attracted many concerns in the industry and academia. It has been reported that every 1.5 C rise in temperature might kill around 70% of the coral reefs and some of the insects may lose their habits [1] These may cause significant environmental and societal problems. To mitigate these problems, many advanced combustion technologies and alternative fuels have been investigated to improve engine performance and simultaneously reduce emissions. The unburned hydrocarbons (UHC) and carbon monoxide (CO) emissions are higher in DF mode [8e10] This reveals a non-optimum utilization of the gaseous fuel in ICEs. The main reason is that the combination of low temperature and very lean natural gas-air mixture inside the combustion chamber for low loads or partial load may lead to incomplete combustion [11,12]. The low power density and abnormal combustion such as knock [15,16], pre-ignition [17] and backfire [14,18] in pure H2-fueled engines have currently limited its usage
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