Effect of Ignition Energy and Hydrogen Addition on Laminar Flame Speed, Ignition Delay Time, and Flame Rising Time of Lean Methane/Air Mixtures

Minh Tien Nguyen,Phu Nguu Do,Van Van Luong,Minh Tung Phung,Quoc Thai Pham

doi:10.3390/en15051940

Minh Tien Nguyen, Phu Nguu Do + Show 3 more

Open Access

https://doi.org/10.3390/en15051940

Copy DOI

Abstract

A series of experiments were performed to investigate the effect of ignition energy (Eig) and hydrogen addition on the laminar burning velocity (Su0), ignition delay time (tdelay), and flame rising time (trising) of lean methane−air mixtures. The mixtures at three different equivalence ratios (ϕ) of 0.6, 0.7, and 0.8 with varying hydrogen volume fractions from 0 to 50% were centrally ignited in a constant volume combustion chamber by a pair of pin-to-pin electrodes at a spark gap of 2.0 mm. In situ ignition energy (Eig ∼2.4 mJ ÷ 58 mJ) was calculated by integration of the product of current and voltage between positive and negative electrodes. The result revealed that the Su0 value increases non-linearly with increasing hydrogen fraction at three equivalence ratios of 0.6, 0.7, and 0.8, by which the increasing slope of Su0 changes from gradual to drastic when the hydrogen fraction is greater than 20%. tdelay and trising decrease quickly with increasing hydrogen fraction; however, trising drops faster than tdelay at ϕ = 0.6 and 0.7, and the reverse is true at ϕ = 0.8. Furthermore, tdelay transition is observed when Eig > Eig,critical, by which tdelay drastically drops in the pre-transition and gradually decreases in the post-transition. These results may be relevant to spark ignition engines operated under lean-burn conditions.

Highlights

The use of alternative fuels, together with lean combustion technology, is an effective way of reducing emissions and enhancing the thermal efficiency of internal combustion engines (ICE) [1–6]
The value of Su0 gradually increases as the hydrogen faction increases from 0 to 20% and is rather rapid when the hydrogen fraction is greater than 20% for three equivalence ratios (φ = 0.6, 0.7, and 0.8)
Tdelay and trising decline in an accelerated tendency with the increase in the hydrogen fraction for the promoted chemical reaction process by more H+, especially when the hydrogen fraction is greater than 20%

Summary

Introduction

The use of alternative fuels, together with lean combustion technology, is an effective way of reducing emissions and enhancing the thermal efficiency of internal combustion engines (ICE) [1–6]. To the best of the authors’ knowledge, experimental studies on the explosion duration characteristics of such lean hydrogen–methane flames over a wide range of hydrogen fraction and ignition energy are sparse. We experimentally investigate the effect of ignition energy (2.4 mJ to 58 mJ) and hydrogen addition (0 to 50% in volume fraction) on the laminar burning velocity and explosion duration characteristics of lean methane/air mixtures at φ = 0.6, 0.7, and 0.8. There are differences from previous studies: (1) the laminar burning velocity is calculated by pressure-rise method; (2) the effect of ignition energy and hydrogen addition on tdelay and trising of lean methane/air mixtures is analyzed for the first time.

Data Processing and Parameter Definition

In-Chamber Pressure Profile and Laminar Burning Velocity Su0

Conclusions