Influence of gaseous fuel induction on the various engine characteristics of a dual fuel compression ignition engine: A review
Introduction
Today's world is mainly relying on CI engines for power generation, especially in the transport sector. Furthermore, the power generation by burning petroleum diesel fuel in CI engines comes at dual crises of fossil fuel depletion and environmental degradation. It is a cogent proof that the combustion of these fuels has a fatal impact on the environment, which leads to deteriorated air quality because of the emission of air pollutants such as oxides of nitrogen (NOx), particulate matter (PM) and secondly, ignites the climate change issue due to the release of carbon dioxide (CO2) into the atmosphere [1], [2], [3]. In fact, India is already the fourth largest greenhouse gas emitter of the world which is expected to reach the top position in the near future [4]. No doubt, the dwindling fossil-fuel reserve, and the environmental pollutants are the well-known pressing issues that need to be addressed today. Fossil fuels, at present, constitute about 80% of the total energy share with almost 50% of it being associated with the transportation sector, which is mainly based on diesel engine [5]. It would be interesting to know that, more than 6.5 million diesel engines exist at present in the Indian farming sector for various activities [6]. Therefore, to address these aforesaid dilemmas, it is imperative to move towards an eco-friendly fuel to power CI engines. The mitigation of greenhouse gas emissions from the environment is the key motivation for the utilization of renewable fuels in CI engine. The worldwide share of renewable energy is about 9% and will rise up to 12% by 2040 [7]. The worldwide automotive fuel consumption in the automotive sector is shown in Fig. 1.
Worldwide research is focussed on appropriate technology as well as alternative fuel that would be used in these existing diesel engines with no or fewer noxious pollutants. Use of sophisticated electronic controllers in CI diesel engine enables reduced emission and better fuel efficiency in comparison to previous counterpart [8]. However, the positive effects of this technology are overshadowed by its high price tag; hence, can’t be commercially employed. In the last few decades, various alternative fuels have been proposed, targeting at cleaner and sustainable energy sources in order to counteract the consequences of the emissions from the CI engines. These include vegetable oil, alcohols, biofuels, compressed natural gas (CNG), natural gas (NG), liquefied petroleum gas (LPG), syngas, methane (CH4), biogas, hydrogen (H2), etc for the replacement of diesel fuels used in CI diesel engine [9], [10]. Studies are being focussed on the usage of gaseous fuels like natural gas for CI engines worldwide, because of their better mixing characteristics with air. Hydrogen is also one of the commonly known clean energy resources; but, discovery of environment friendly technique to produce H2 at a lower price is the challenging task for research.
Indeed, there are review articles published on different strategies and alternatives fuels for CI engines; with some reviews on blending of additives with biodiesel [11], [12]. Rajasekar and Datta et al. [13], [14] published reviews on CI engines fuelled with biodiesel; their monumental study set a milestone in the field of CI engines. Debnath et al. [15] reviewed the application of emulsion as an alternative fuel. Singh et al. [16] discussed about a methodology for the complete elimination of diesel fuel in their review. Varun et al. [17] reviewed on the studies based on the modification of combustion chamber geometry. Given a multitude of these reviews, it is an apt time to make an attempt to compile and analyze the research studies focussing on the influence of potential gaseous fuels (like H2, biogas, syngas) induction on the combustion, performance and emission characteristics of a dual fuel CI engine. The emphasis of the current review is the exploration of new alternative and clean renewable fuels to be used in conjunction with diesel in existing CI engines without major modifications.
Section snippets
Gaseous fuel as an alternative fuel
Gaseous fuels have been emerging as attractive alternative energy resources to replace diesel fuel either partially or completely in CI engine. The injection of gaseous fuel in CI engine under dual fuel mode is not a new technology; it has been investigated by many researchers with widespread success [18], [19]. Usually, gaseous fuel is mixed with the intake air during the suction stroke of dual fuel CI engine, either through manifold injection or through direct injection into the cylinder [20]
Conclusions
Reviewing various studies on the utilization of gaseous fuels (especially H2, biogas and syngas) with diesel/biodiesel as pilot fuel in dual fuel CI engine reveals the following:.
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H2 has higher laminar flame speed, shorter ignition delay and lower minimum ignition energy that enhance flame propagation process and initial flame development inside the cylinder.
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Large number of studies reported improvement in engine performance in terms of BTE and brake power with increase in H2 energy share in dual
Future scope
Although, this detailed literature review highlighted the use of H2, biogas and syngas in CI engine under dual fuel mode, but there are certain allied areas which needs further attention:
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H2 energy, additionally to hydro, biomass and solar, is also one of the long term renewable fuel. Nevertheless, the technologies for H2 production at an affordable cost and safe storage are the great challenges for the utilization of H2 in CI engines. Moreover, the transportation of H2 needs standards related
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