The biofuel can be a sustainable option to reduce the global warming caused by the greenhouse gas (GHG) emissions as a replacement of fossil fuels. Looking for this replacement, in Brazil, the Proálcool Program encourages the production of bioethanol from sugarcane to feed light-duty vehicles with flex spark-ignition engines. Brazil presents a relevant potential to produce biofuels, taking advantage of the conversion of organic wastes generated in the agroindustry. Also, Brazil has a mainly renewable electrical matrix, which 64.9% of the electricity generated comes from hydroelectric plants (EPE, 2020a), which gives the advantage to implement electric vehicles in its fleet. In 2019, the renewable sources were responsible for 46.1% of the internal energy supply in Brazil, such as hydraulic power, wind power, solar power, sugarcane sources and biodiesel (EPE, 2020a). The energy consumption of the transport sector increased in 3.3% in 2019, due to the use of biofuels, totalizing 25%. However, the most used fuels were gasoline (25.3%) and diesel oil (41.9%). Despite the low consumption of biofuels, Brazil is ahead of other member countries of the Organization for Economic Cooperation and Development (OECD), which presented 5% use of renewable fuels in the transport sector in 2017 (EPE, 2020a).
The electric vehicles (EV) are also an alternative to decrease the negative environmental effects caused by the fuel consumption. The plug-in hybrid electric vehicle (PHEV) is a type of EV that can be an alternative to reduce the GHG, once it can operate using an electric motor powered by the lithium-ion (Li-ion) battery or by the internal combustion engine (ICE). However, the components of the different types of EV, in this case the PHEV, have advantages and disadvantages. The Li-ion battery presents advantages such as higher power and energy densities, and longer battery life than the other battery types. This battery type is selected because of its low self-discharge rate, which means the amount of charge lost when the battery is not used, and the absence of the memory effect, phenomenon that occurs in older batteries compound by NiCd, basically, making them to acquire a charge capacity less and less, when a proper care in recharging is not carried out. But the disadvantage is that the Li-ion battery its cost is relatively higher than the other battery types. However, the manufacturing cost of the these batteries tends to decrease due to several factors, i.e., mass production, and its cost reduction will reinforce the importance of the renewable energy as an alternative to fossil fuels that aggravates the negative impacts to the environment and human health (Asif and Singh 2017). On the other hand, the ICE operates with fossil fuel or biofuel and can be classified as Otto cycle (spark-ignition), in which the fuel-air mixture is injected in the chamber and the combustion is made by the spark valve, or Diesel cycle (compression-ignition), which the ignition is caused when the fuel is sprayed in the chamber after the air is compressed. Although, focusing on decrease the GHG emissions caused by the PHEV, two point needs to be considered: first, the electricity that power the electric system have to be renewable, but it depends on the electricity source prevalent in each region; second, the ICE needs to be fuelled with biofuels, such as bioethanol and biogas once they cause lower negative effects than the fossil fuels, or adapting the ICE to operations in dual-fuel mode. The dual-fuel mode is a technology projected to burn two fuels at the same time. In this mode, an ICE (Otto or Diesel) is adapted to inject a gaseous fuel with air through the port injection, and a liquid fuel through a valve inside the chamber. This can reduce the environmental impact caused by the tailpipe emissions, once a percentage of more pollutant fuel can be replaced with a percentage of a less pollutant fuel. To make the use of the PHEV in dual-fuel mode viable, the TTW emissions of the engine must be low when compared to the tailpipe emissions standards recently provided by the European community (95 gCO2/km by 2021 and 59 gCO2/km by 2030 – IEA) and by the United States (89 gCO2/km by 2024 – EPA).
In this study, the series PHEV Chevrolet Volt will be analysed. In general, the series PHEV presents differentiated operating modes, depending on the battery state of charge and driver’s requests. The main modes are charge-sustaining (CS) mode; charge-depleting (CD) mode; EV mode and ICE mode (Singh et al. 2019). In the CS mode, the ICE is the main power source, and the battery state of charge is controlled to stay within a limit between 30% and 40%, depending on the battery type and the vehicle, to avoid any damage on the battery and decreasing of its number of recharge cycles. On the other hand, in CD mode, the battery is the main power source, and its state of charge is controlled to decrease during the operation of the vehicle. In this mode, the battery needs the power supplied by the ICE to meet the driver’s requests, and the battery loss is greater, which can reduce its lifetime. In EV mode, the series PHEV operates as a battery electric vehicle (BEV), being powered exclusively by the battery. Finally, in ICE mode, the series PHEV operates as an internal combustion engine vehicle (ICEV), consuming fuel to generate power (Singh et al. 2019).
The grid-to-vehicle (G2V) power and the possibility of bidirectional power through vehicle-to-grid (V2G) was investigated, i.e., to eventual residential supply. Mumtaz et al. (2017) developed a study about energy management and control system of charging station for PHEV, considering among other cases G2V and V2G. Hu et al. (2017) analysed the V2G interaction and its potential impact on the PHEV economy, and concluded that the battery aging cost induced by the V2G outweighs the V2G-added revenue, requiring subsides from the grid to counterbalance this cost. Besides that, the use of algorithm construction methods has been studied by several articles for solving computational problems of combinatorial optimization such as dynamic programming. Wang and Liang (2017) applied the dynamic programming to formulate the energy management for PHEV via bidirectional V2G, aiming to minimize the daily energy cost. Zhang et al. (2017) conducted a study about power management in a PHEV using dynamic programming to optimize the control strategy in the model predictive control. The studies was also directed to the use of Li-ion battery in PHEV (Asif and Singh 2017; Lopez-Sanz et al. 2017), its degradation and its influence on fuel consumption (Cai et al. 2017).
To evaluate or compare the environmental impact caused by the PHEV and other EV types, and ICEV, the GHG emissions were analysed. De Souza et al. (2018) investigated the characteristics of PHEV, ICEV and BEV to analyse their environmental performance. According to the results, the PHEV and the ICEV presented similar environmental impact since they use ethanol or gasoline as fuel. Otherwise, the PHEV and the BEV presented higher results for human toxicity potential, because of the impact of the Li-ion battery production, but PHEV shows better results than BEV because of the lower weight of the battery (Souza et al. 2018). Also, the GHG emissions depend on the electricity grid mix and of the vehicle usage (Plötz et al. 2018).
Some studies related to life cycle assessment of the PHEV were published. De Souza et al. (2018) carried out a life cycle assessment to assess the well-to-wheel (WTW) for ICEV, PHEV and EV. The authors considered the ICEV with ICE powered by E25 gasoline, mixture of ethanol and gasoline (flex fuel vehicles), and ethanol, the PHEV with the ICE powered by gasoline, and the pure EV powered by electricity. The results showed that the ICEV fuelled with gasoline and in flex-mode presented the highest global environment impacts and suggested to analyse the impact categories isolated. Chen et al. (2018) investigated the life cycle CO2 emissions of the PHEV and the BEV, through their performance and energy consumption over a four-month period and concluded that when the vehicles were in high speed or high acceleration conditions, the distance-normalized life cycle CO2 emissions of PHEV and BEV were higher then ICEV fuelled with gasoline. In the studies found, none analysed the life cycle assessment of the biogas and bioetanol from sugarcane through a detailed simulation on GREET software, considering the losses during the production process and its Well-to-Pump emissions.
In the case of dual-fuel mode, studies were directed to analyse its characteristics applied in ICEV with Otto cycle or Diesel cycle. Niu et al. (2016) studied the use of gasoline enriched with hydrogen in the Otto cycle, and concluded that flame developing duration and combustion duration were reduced with the addition of hydrogen in gasoline. Chen et al. (2019) evaluated the Otto cycle fuelled with methanol and natural gas in dual-fuel mode. According to the results, the methanol induced to a faster burning rate, improved the brake thermal efficiency, and reduced the equivalent brake specific fuel consumption. In case of Diesel cycle. Shan et al. (2016) investigated the effects of exhaust gas recirculation on combustion and emission characteristics of the Diesel engine fuelled with direct-injected diesel and port-injected biogas. The results showed that, when the exhaust gas recirculation rate increases, the combustion phase retards and the ignition delay in the engine gets prolonged. Karagöz et al. (2016) conducted a study using port-injected hydrogen and direct-injected diesel in the Diesel cycle and concluded that the brake thermal efficiency was decreasing with the increase of hydrogen in the mixture.
Up to date from preview literature review, no scientific works were published analysing dual-fuel mode in the PHEV using biofuels. To address this gap, this study aims to evaluate the possibility of replacing the single-fuel spark-ignition engine (SFSIE) of the series PHEV Chevrolet Volt II Generation powered by gasoline with the ICE powered by biogas and bioethanol from sugarcane, operating in dual-fuel mode. For this analysis, the Well-to-Wheel (WTW) emissions will be analysed through the Well-to-Pump (WTP), Tank-to-Wheel (TTW) emissions and electricity mix emissions. The energy efficiency of the Chevrolet Volt operating modes will also be analysed, and the energy-ecological efficiency of the ICE fuelled with different fuels in single-fuel and dual-fuel mode will be determined. Also, the bioethanol and biogas mass flow will be calculated for operation in dual-fuel mode. It is expected that the contributions of this article will fortify the environmental criteria that can enable decision-making to promote more sustainable end environmentally friendly vehicle technologies.