Nanofuels: Combustion, engine performance and emissions

doi:10.1016/j.fuel.2013.12.008

Fuel

Volume 120, 15 March 2014, Pages 91-97

https://doi.org/10.1016/j.fuel.2013.12.008 Get rights and content

Highlights

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Stable suspensions of nanoparticles of Al, Fe and B in diesel were used as fuels.
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These fuels showed reduced ignition delay, and longer flame sustenance.
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Specific fuel consumption reduced by 7% with nanoparticle modified fuels.
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Emissions of CO and hydrocarbons reduced, however NO_x marginally increased.

Abstract

Experimental investigation was carried out to study the burning characteristics, engine performance and emission parameters of a single-cylinder Compression Ignition (CI) engine using nanofuels which were formulated by sonicating nanoparticles of aluminum (A₁), iron (F₁) and boron (B₁) in base diesel. These fuels showed reduced ignition delay, longer flame sustenance and agglomerate ignition. Study of engine performance at higher loads revealed drop in peak cylinder pressures and reduction of 7% in specific fuel consumption for A₁ as compared to diesel. Improved combustion rates raised exhaust gas temperatures by 8%, 7% and 5% leading to increased brake thermal efficiencies by 9%, 4%, and 2% for A₁, F₁, and B₁ respectively, as compared to diesel at maximum loading conditions. Volumetric reduction of 25–40% in CO emission, 8% and 4% in hydrocarbon emission was measured when the engine was fueled with A₁ and F₁ respectively as compared to emissions from diesel. However, elevated temperatures resulted into marginal rise in NO_x emission.

Introduction

Application of nanoscale energetic metal particle additives in liquid fuel is an interesting concept yet unexplored to its full potential. Such formulated nanofuels offer: shortened ignition delay, decreased burn times and rapid oxidation which leads to complete combustion [1], [2], [3]. Overall calorific value of the liquid fuel increases due to higher energy density of metal particles, eventually improving the performance of engine by boosting power output. The study of evaporation rate and ignition probability plays an important role in determining two critical properties: ignition delay and ignition temperature which characterizes the performance of a diesel engine and are also instrumental in curtailing emissions [4]. Reports have shown that fuels blended with nanoparticles of aluminum, boron or carbon particles enhance ignition probability at lower temperatures as compared to diesel and initiate combustion thereby reducing ignition delay [5], [6], [7], [8]. A crucial phenomenon involved in improving the combustion rate of the nanoparticle blended fuels is the disruption/microexplosion behavior of the fuel droplets and was first discovered by Takahashi et al. [9] for slurries of boron/JP-10. This behavior was also evidenced by a few other studies involving aluminum, boron, iron and carbon slurries [10], [11], [12], [13]. In order to ensure the feasibility of these derived fuels as commercial substitutes of conventional fuels, they were tested in diesel engine. Cited studies have shown reduced brake specific fuel consumption, smoke and NO_x formation with combustion of Al-nanofluid in Compression Ignition (CI) engine [14], [15]. Aluminum nanopowder when blended with water/diesel emulsion fuel reacts with water at higher temperatures and generates hydrogen which promotes combustion in engine chamber [16].

Present investigation is focused on incorporating energetic metal nanoparticles of aluminum, iron and boron in petro-diesel as additives to accelerate combustion rates, reduce ignition delay, and boost calorific values. Engine performance, emissions and combustion attributes of CI engine also have been studied. The ensuing section aims to (i) determine the evaporation rates and ignition probability of the formulated and stabilized nanofuels (ii) study different combustion stages to explore the burning mechanism of the nanofuel droplets, (iii) study performance characteristics of single-cylinder four-strokes Compression Ignition engine with nanofuels and compare them with diesel and (iv) examine emissions and soot produced to investigate their environmental impact.

Section snippets

Fuel formulation

Stable and homogeneous suspension of iron, aluminum and boron (Nanoshel LLC, USA) in base diesel was made using ultrasonication (Sonics Vibra cell-USA, 750 W, 20 kHz) for 15 min, and addition of the surfactant Span80^™ (Qualigen Chemicals, Mumbai, India). The most stable nanofuels with maximum particle loading were selected on the basis of backscattering profiles (Turbiscan classic MA 2000 (Formulaction, France). Compositions of the fuels was nanoparticles (n-Fe, n-Al or n-B) 0.5 wt%, Span80 (0.1

Droplet combustion mechanism

When drops of diesel and nanofuels were made to fall onto the heated steel plate, the diesel present in samples vaporized soon leaving behind oxide coated nanoparticles which were than exposed to higher chamber temperatures. It was noted that above 700 °C, the oxide layer onto the metal surface of nanoparticles vanished thereby exposing the same to higher temperatures which lead to various sequential combustion stages. Fig. 2 depicts a sequence of pure diesel droplet formation, disruption and

Conclusions

Nanofuels A₁, B₁ and F₁ showed increased evaporation rates with early ignition at 0.2 s as compared to diesel (1.2 s), suggesting reduced ignition delay. On ignition of A₁ and F₁ droplets, flame sustained for longer period of time followed by ignition of agglomerates coated with un-burnt nanoparticles which was not observed during the burning of diesel and B₁ droplets. Peak cylinder pressures decreased at full load conditions and were registered as 55, 59, 60 and 62 bars for A₁, B₁, F₁ and diesel

Acknowledgements

Authors thank Dr. P.V. Bhale, Mechanical Engineering Department, SVNIT, Surat for kindly extending their facilities for some of the tests and meaningful discussions.

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View full text

Nanofuels: Combustion, engine performance and emissions

Highlights

Abstract

Introduction

Section snippets

Fuel formulation

Droplet combustion mechanism

Conclusions

Acknowledgements

Proc Combust Inst

Prog Energy Combust Sci

Combust Flame

Combust Flame

Combust Flame

Int J Heat Mass Transfer

Combust Flame

Combust Flame

Combust Flame

Prog Energy Combust Sci.

Internal combustion engine fundamentals