Effects of a wave-shaped piston bowl geometry on the performance of heavy duty Diesel engines fueled with alcohols and biodiesel blends
Introduction
Replacing fossil fuels with renewable biofuels could greatly reduce vehicles’ well-to-wheel greenhouse gas (GHG) emissions and thereby help vehicle manufacturers comply with increasingly stringent regulations [1]. For instance, replacing fossil Diesel with n-butanol, isobutanol, n-octanol, or 2-ethylhexanol derived from non-food biomass could reduce well-to-tank equivalent carbon dioxide (CO2) emissions by 65%, 50%, 56%, and 62%, respectively [1,2]. Because of this potential to reduce lifecycle GHG emissions, there is great interest in using renewable longer-chain alcohols as alternative fuels for Diesel engines. Rakopoulos et al. [3] showed that replacing fossil Diesel with n-butanol/Diesel blends in a Diesel engine can reduce soot formation because such blends form overall ‘leaner’ fuel-air mixtures than conventional Diesel fuel. This reduction in soot formation is not accompanied by a significant increase in (NOx) emissions, offering a way to avoid the soot-NOx trade-off. Yao et al. [4] showed that using Diesel/n-butanol blends in conjunction with pilot- and post-injection strategies effectively reduced soot emissions from a heavy duty (HD) Diesel engine. However, the combined positive impact of using the blended fuels and the multiple-injection strategy was lower than expected based on their individual effects. Additionally, increasing the exhaust gas recirculation (EGR) rate amplified differences in heat release between butanol isomers, and therefore also amplified differences in emissions [5]. Higher percentages of n-butanol blends are able to achieve longer ignition delay and partially premixed combustion, reducing soot emissions further and showing the potential of high thermal efficiency [6,7]. Like other drop-in alcohols, pure n-octanol and its blends yielded a higher thermal efficiency and lower soot emissions than Diesel because of its oxygen content and higher latent heat of evaporation, which may reduce heat losses by decreasing the cylinder temperature [8,9].
The use of bio-based fuels such as hydrotreated vegetable oil (HVO) and rapeseed methyl ester (RME) in Diesel engines has been studied extensively. Replacing fossil Diesel with HVO in HD engines reduced NOx, soot, CO and HC emissions over a wide range of operating conditions [10,11]. However, under the same operating condition with same engine settings, the rate of heat release curves generated using HVO differed from those of fossil Diesel [12].
Piston bowl geometry strongly affects in-cylinder air motion because it influences the development of the complex turbulent flow field at the end of the compression stroke [13]. Simulations and experimental studies [14,15] have been done to prove that the diameter ratio of the piston bowl and cylinder bore influences the velocity field. Due to the different properties of biofuel compared with fossil Diesel, the optimization of injection timing and piston bowl geometry improves the thermal efficiency and reduces the emissions for the biofuel application [16]. A wave-shaped piston [17] was recently shown to improve late-cycle air mixing during diffusion combustion by efficiently guiding the near-wall jet flow back towards the chamber center. Increasing the level of turbulence in the reaction layer improves fuel-air mixing and promotes faster and more complete combustion, increasing thermal efficiency and thus reducing soot emissions. However, it is not yet known how the use of the wave piston affects emissions and thermal efficiency when using fossil-free fuels.
The aim of this study is therefore to evaluate the performance and emissions of HD engines with wave pistons when burning blends of various oxygenated fossil-free fuels, and to compare the wave piston’s effects to those of a conventional omega piston design. Combustion experiments were performed using fossil-free fuels including blends of n-butanol, n-octanol, 2-ethylhexanol, HVO, and RME, using typical production engine settings. To ensure that the ignition delay time was similar in all experiments, the CN values of the tested blends were adjusted to match that of fossil Diesel. Combustion experiments were also performed using fossil Diesel as a reference fuel. The combustion characteristics and engine out emissions achieved with the wave and conventional (omega) piston designs were compared using fossil Diesel and an n-butanol/HVO blend under the same engine settings as in the other combustion experiments.
Section snippets
Fuel properties
The fossil-free fuels tested in this work were blended by HVO, n-butanol, n-octanol, 2-ethylhexanol, and RME. Fossil Diesel was used as a reference fuel. Table 1 shows the properties of these fuels. Fossil Diesel satisfying the EN590 standard and containing no fatty acid methyl ester (FAME) was used. FAME blends used in commercial Diesel fuels are mainly synthesized from animal fats and some vegetable oils by esterification [18]. A commonly used FAME in the Swedish market is RME, which has very
Engine combustion characteristics when using the wave piston
Fig. 3 shows the apparent rate of heat release curves at A25, B50, C75, and B75 for the single cylinder HD engine. For all operating points, the rate of heat release profiles of the fossil-free blends closely resemble that of fossil Diesel. The variation between the fuels with respect to the timing of the start of combustion (SOC), i.e. the moment at which the heat release rate cross zero from negative, was less than 0.5 crank angle degrees (CAD) at each load point. This confirms that using
Conclusions
This paper investigated the effect of using a wave-shaped piston bowl on the performance and emissions of a heavy-duty Diesel engine (with factory-calibrated engine settings) fueled with conventional Diesel fuel and various fossil-free alcohol blends. The blends contained n-butanol, isobutanol, n-octanol, and 2-ethylhexanol, together with HVO and RME, and their cetane numbers were adjusted to match that of fossil Diesel.
When using the wave piston, the fossil-free blends and fossil Diesel
Acknowledgements
This work was performed as a part of the project -Butanol as an alternative fuel for Diesel engines, which is supported by the Swedish Energy Agency, Perstorp AB, Scania CV, Neste, Volvo GTT and Volvo Cars. The financial and technical support of these organizations is gratefully acknowledged. The authors would also like to thank Dr. Timothy Benham for his assistance and technical support during the experiments.
References (36)
- et al.
Progress in the production and application of n-butanol as a biofuel
Renew. Sustain. Energy Rev.
(2011) - et al.
Investigation of the performance and emissions of bus engine operating on butanol/diesel fuel blends
Fuel
(2010) - et al.
Experimental study of n-butanol additive and multi-injection on HD diesel engine performance and emissions
Fuel
(2010) - et al.
Experimental study on diesel conventional and low temperature combustion by fueling four isomers of butanol
Fuel
(2015) - et al.
Investigation into partially premixed combustion fueled with n-butanol-diesel blends
Renew. Energy
(2016) - et al.
The comparison of particle oxidation and surface structure of diesel soot particles between fossil fuel and novel renewable diesel fuel
Fuel
(2010) - et al.
Investigation of piston bowl geometry and speed effects in a motored HSDI diesel engine using a CFD against a quasi-dimensional model
Energy Convers. Manag.
(2010) - et al.
Combined effect of injection timing and combustion chamber geometry on the performance of a biodiesel fueled diesel engine
Energy
(2012) - et al.
Role of fuel properties and piston shape in influencing soot oxidation in heavy-duty low swirl diesel engine combustion
Fuel
(2019) Biofuels sources, biofuel policy, biofuel economy and global biofuel projections
Energy Convers. Manag.
(2008)
The effect of the addition of individual methyl esters on the combustion and emissions of ethanol and butanol -diesel blends
Energy
Effect of using butanol and octanol isomers on engine performance of steady state and cold start ability in different types of diesel engines
Fuel
Soot in diesel fuel jets: effects of ambient temperature, ambient density, and injection pressure
Combust. Flame
Effects of current engine strategies on the exhaust aerosol particle size distribution from a heavy-duty diesel engine
Aerosol Sci.
Combustion performance and pollutant emissions analysis using diesel/gasoline/iso-butanol blends in a diesel engine
Energy Convers. Manag.
An experimental study on the combustion and emission characteristics of a diesel engine under low temperature combustion of diesel/gasoline/n-butanol blends
Appl. Energy
A Comparison Of Drop-In Diesel Fuel Blends Containing Heavy Alcohols Considering Both Engine Properties And Global Warming Potentials
Combustion Characteristics For Partially Premixed And Conventional Combustion Of Butanol And Octanol Isomers In A Light Duty Diesel Engine
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2023, FuelCitation Excerpt :In this way, the flame could reach zones of the combustion chamber around the injector where fresh oxygen is still available. In addition, this movement avoids the flames to spread tangentially, reducing the flame-to-flame collision and the formation of fuel rich zones [19], where soot is formed. Volvo reported a significant reduction of soot emissions (around 80 %) as well as a faster burn out [20], opening a door to achieve soot reductions without penalizing the NOX emissions (NOX-soot trade-off reduction).