CNG Buses Research Articles

Study on the Emission Characteristics of Typical City Buses under Actual Road Conditions

Five typical in-use city buses in Tangshan with different emission standards, fuel power types, and emission control technology routes were selected as the research objects. PEMSs (Portable Emissions Measurement Systems) and OBD (On-Board Diagnostic) remote monitoring technologies were used to conduct research on actual road conditions and emission characteristics. The research aimed to analyze the driving characteristics of different power types of bus engines and after-treatment systems, as well as their impact on emissions. The results indicated that the actual road driving is mainly in the urban and suburban areas of the local region. Additionally, the VSP (Vehicle Specific Power) was found to be distributed in the low- and medium-speed range of mode Bin0~Bin24. The emission rates of each pollutant showed an increasing trend with the increase in VSP. THC and NOx emissions of CNG and LNG buses are significantly higher than those of gas–electric hybrid buses. However, the PM emissions are lower. Therefore, it is necessary to strengthen the NOx emission control of CNG and LNG buses. With the improvement in emission standards and the use of hybrid technology, CO2 and NOx emissions of China IV buses can be reduced by 13% and 53.5% compared with China III buses of the same tonnage. The CO2 and NOx emissions of China V buses using natural gas combustion and an electric mixture are 20% and 18.8% lower than those of China V buses of the same tonnage using only natural gas. In the actual operation of the diesel–electric hybrid bus equipped with the SCR (Selective Catalytic Reduction) system, the working time of the engine is about 35.5 ± 5%, and the working time of the SCR system only accounts for 65.5 ± 12%. The low working conditions of the SCR system and the low temperature of SCR system are the reasons for the high NOx concentration at the rear end of the SCR system when the hybrid electric bus is running at low speeds.

Pathway of reducing CO2 emission and harmful exhaust gases in transport by using electric buses-the example of Belgrade

The buses have an irreplaceable role in the public transport system, regardless of city size. Buses powered by internal combustion engines (diesel, CNG) are still the most common concept of city buses, but in the last few years, the use of fully electric buses (E-buses) has been growing. One of the reasons for the increasing use of electric buses is their environmental advantages over conventional buses: zero emissions at the local level (Tank-To-Wheel) emission, more favourable carbon dioxide (CO2) emissions at the regional or national level (Well-To-Wheel), and higher energy efficiency. The EKO1 line (Vukov Spomenik-Belvil) has operated in Belgrade since 2016, with five full electric buses. The paper will present the environmental aspects of using electric buses on line EKO1 compared to diesel and CNG buses. The environmental aspects of E-buses were researched through the effects of reducing the emission of harmful exhaust gases caused by eliminating the use of diesel-powered or CNG-powered buses and introducing E-buses. Within the ecological suitability of the using E-buses, the emission of carbon dioxide (CO2) that occurs indirectly during electricity production was researched and a comparison was made with the emissions of CO2 caused by the combustion of diesel fuel and CNG in buses with conventional propulsion. The paper also examined the energy efficiency of buses with different drive systems on the line EKO1, based on the analyzed energy consumption. As a result of the analysis, the introduction of electric buses on the EKO1 line was justified from the point of view of improving the environment through the reduction of harmful gas emissions and decarbonization as well as better energy efficiency.

An Adaptive Battery Charging Method for the Electrification of Diesel or CNG Buses as In-Motion-Charging Trolleybuses

The decarbonization of urban bus fleets can be made by their electrification as In-Motion-Charging (IMC) buses which can run both as trolleybuses or in battery-mode. The benefit is that IMC buses can use the existing trolleygrid infrastructure where their route overlaps with it to charge the battery, and operate in battery-mode outside of it. Presently, the IMC battery charging power is set conservatively to the minimum of all the spare capacities of the traction substations found along the bus route. This can render most electrification projects techno/economically infeasible as not enough energy is picked up for the battery-mode operation and long charging times at bus terminals are required. This paper proposes then an Adaptive Charging approach that uses the locally available spare capacity under any traction substation, taking into account the limitations of the maximum substation power and the minimum line voltage. The method is proven here both theoretically and in a case study over one full year of operation of four electrified diesel/CNG bus lines in Arnhem, the Netherlands, using comprehensive and verified trolleybus and trolleygrid models. The proposed Adaptive Charging method, as opposed to the present conservative method (here, Regular Charging), is shown to make one bus electrification project completely feasible, and reduce the extra terminal charging time for the other lines by up to 64%.

Emission factors and fuel consumption of CNG buses in real driving conditions

Emission factors and fuel consumption of CNG buses in real driving conditions

전기철도 배전망을 활용한 팬터그래프 방식 충전시스템에 관한 연구

In the industrial fields have being accelerated the development of alternative energy resources because of restriction of environment pollution and increasing oil price at the world. Most of conventional vehicles are reason of environment pollutions. For these reason, interest in electric vehicles are increasing because of which is solution of reducing the environment pollution issues. Although a local autonomous entity had tried to replaced CNG buses for operating electrical buses, electrical buses have intrinsic problems such as charging/discharging sequences, connector issues and charging time. For these reason pantograph-type automatic charging technology is being developed for mating the environment of bus garages in nation. However, that has some problems such as initial price, room of charging infrastructure and electric power supply. In this paper, therefore, proposes methodology of using railway power supply system. It has been verified under suitability and balidity of charging and discharging scenario using electric bus charging system simulation model based on MATLAB Simulink and PSIM.

Economic Assessment of Investment in Electric Buses and CNG Buses – A Case Study of a Public Transport Company

Economic Assessment of Investment in Electric Buses and CNG Buses – A Case Study of a Public Transport Company

Comparison on real-world driving emission characteristics of CNG, LNG and Hybrid-CNG buses

This study used a portable emission measurement system (PEMS) to investigate the emission characteristics of three Euro V buses (a CNG bus, an LNG bus and a hybrid-CNG bus) under real-traffic conditions. The results showed that the emission factor of gaseous pollutants decreased gradually with increasing driving speed. The LNG bus showed the highest emission characteristics, especially the emissions of CO, NOx, PM and BC. Although the NOx emission factor for the LNG bus was the highest (23.56 g/km), its NO2 emission factor (0.82 g/km) was lower than that of the CNG bus (1.58 g/km). Moreover, the particle size of the particulate matter emitted by the LNG buses was large, and the ratio of BC/PM was about 40%, which was much higher than those of the other two buses (7.59% and 33.11% for the CNG bus and hybrid-CNG buses, respectively). Compared with the CNG bus, the hybrid-CNG bus could effectively reduce particle number emissions by 59.1%, mainly by reducing the emission of nucleation-mode particles with particle size less than 30 nm. However, the emissions factors of other pollutants of the hybrid-CNG bus were higher than those of the CNG bus, especially the emission of black carbon, which was 66% higher.

Comprehensive Total Cost of Ownership Framework for Alternative Fuel Public Transportation Buses

Sustainable fleet management seeks to deliver the best service with a standard of service defined by state regulatory bodies by utilizing and managing large fleets of vehicles in the most efficient, productive, and cost-effective way. Public transport service providers thus seek alternative ways to minimize cost as well as air pollution and carbon emissions from the transportation sector. This study develops a total cost of ownership (TCO) framework for evaluation of different alternative fuel options (diesel, compressed natural gas [CNG], and electric) for bus public transportation based on real-world driving conditions. Electric, CNG, and diesel buses are compared from the life cycle perspective by quantifying a set of sustainability indicators including global warming potential, particulate matter formation, human health impacts, and TCO. According to the results, it was found that TCO of electric buses is less than that of diesel and CNG buses. Specifically, TCO of electric buses is 15% less than that of diesel buses, and compared with CNG it is 5% less over a period of 10 years of use. The proposed framework provides a quantitative basis for a sustainable fleet management approach for public bus service providers.

Evaluation of the impact of ambient temperature on fuel consumption by diesel and CNG buses

The paper is devoted to the problem of bus operation in various climatic, road and transport conditions. The reasons for replacing diesel buses with more environmentally friendly ones using natural gas are described. Experimental studies on the operation of large-class buses –LiAZ-529265 diesel bus and LiAZ-529267 CNG bus in an urban environment are given. The dependences of the influence of various ambient temperatures on fuel consumption are obtained, and mathematical models that describe these dependences are proposed. The range of studied temperatures is from minus 31°C to +37°C. As a result of drivingexperiments, it was found that the natural gas consumption of the LiAZ-529267 bus is 23-24% higher than that of the diesel counterpart under similar road and transport operating conditions. The deviation between the minimum and maximum values of diesel fuel consumption is 37-45%. For compressed natural gas, the deviations were 36-43%. However, the equivalent cost of purchasing natural gas is 52% lower than that of diesel fuel.

Comparison on Real Driving Emission Characteristics of Cng, Lng and Hybrid-Cng Buses

Comparison on Real Driving Emission Characteristics of Cng, Lng and Hybrid-Cng Buses

Challenges to Alternative Fuel Vehicle Usage in Trinidad

The Government of the Republic of Trinidad and Tobago has set itself some lofty targets in terms of reducing CO2 emissions from public transportation by 2030. Several initiatives have been launched since 2015 in order to fulfill these targets. One key strategy is the adoption of a higher percentage of alternative fuel vehicles (AFVs) into the overall fleet of vehicles. This article reviews the history and implementation of the various AFV oriented policies and examines the effectiveness of these initiatives. The authors describe the current state of the motorised vehicle fleet in terms of fuel type and highlight where adoption levels have fallen short of the target. The percentage of AVFs per public transit mode ranges from about 2 to 20 percent, where the higher percent represents the CNG buses belonging to the Public Transport Service Corporation (PTSC). In Trinidad, the natural gas supply is already well-established, refuelling stations are in operation and up to 20 original equipment manufacturer CNG vehicles are available on the market, supplemented by the option of vehicle conversion. The opposite is true for electric vehicles. The article further identifies the four key issues affecting the improved adoption of AFVs namely: (i) Fuel Prices (ii) Availability of Alternative Fuels, (iii) Consumer Perception and Resistance, and (iv) Lack of Institutional Support. In addition to presenting the proposals by others for improvements to the local transportation system, the authors recommend six key actions that should be taken to achieve the targets set for 2021 and beyond.

Assessment of investment in electric buses: A case study of a public transport company

Abstract This case study presents an assessment of the efficiency and risk of the vehicle fleet renewal in the public transport company. The investment project is solved in two alternatives. The first alternative consists of vehicle replacement by only electric buses. In the second alternative, a combination of electric buses and CNG buses is considered. Assessment of the economic efficiency of the investment project is based on the net present value (NPV). Due to lower initial and ongoing capital expenditures, the second alternative is more cost-effective than the first one although the profitability of the investment project is low. Within risk assessment, sensitivity analysis points out the subsidy and personal costs as the risk factors influencing variance of NPV the most. Finally, the effectiveness of the investment project is assessed at different levels of the use of financial support from EU funds and the state budget. In that case, even a low level of financial support significantly increased the profitability of the project.

Estimating gaseous pollutants from bus emissions: A hybrid model based on GRU and XGBoost

In urban areas, traffic-related contamination is one of the main contributors to environmental deterioration, and the pollution from public transit buses is a major component. To mitigate these impacts, it is essential to estimate bus emissions and analyze their characteristics. This paper proposes a hybrid model based on gated recurrent unit (GRU) and extreme gradient boosting (XGBoost), termed GRU-XGB, to predict gaseous pollutants from bus emissions (CO, CO2, HC, NOX) under real conditions. On-road experimental data collected from CNG-fueled and diesel-powered buses in Zhenjiang was used as a case study to verify the model's effectiveness. A comparison between the proposed and other state-of-the-art models reveals that GRU-XGB performs best for all evaluation metrics on both microscopic and aggregative levels, with an average correlation coefficient above 0.98 and an average MAPE lower than 9%. Moreover, the results of estimation errors analysis suggest that the real conditions of bus stations are more complicated than those of intersections and road sections. In most cases, however, the emission factors produced from intersections are proven to be the highest. Furthermore, operating patterns are shown to be the most significant factors, with relative importance equal to 45.09% and 71.68% for CNG and diesel buses, respectively. Besides, the results also indicate that humidity has little impact on this issue, while the influence of temperature is obvious, with relative importance equal to 17.56% and 9.41% for CNG and diesel buses, separately. Such findings can provide theoretical guidance for both emission estimation and environmental protection. Also, it is applicable for the management of accurate monitoring from an urban-level and can be integrated into emission simulation tools.

Comparison of real driving emissions from Euro VI buses with diesel and compressed natural gas fuels

Public transport bus service is extended in big cities and cleaner bus fleets are encouraged to reduce greenhouse and air pollutant emissions in high populated areas. In this work, real driving emissions produced by two Euro VI-C buses, one fueled by diesel fuel and one fueled by compressed natural gas, were measured. Both vehicles with different engine technologies but with the same pollutant emission certification, were tested in Madrid (Spain), in order to compare their emissions under the same route. The buses were instrumented with a modular on-board Portable Emissions Measurement System, the OBS-ONE by Horiba. Regulated gaseous emissions and particle number were registered together with different vehicle parameters: speed, exhaust mass flow rate, air and fuel consumption, environmental conditions and global position coordinates during the route. THC emissions from CNG bus doubled those obtained with Diesel bus. Slightly higher NOx emissions from the Diesel bus, with selective catalytic reduction, were obtained during those parts of the circuits (mainly urban) where both the exhaust and the operation temperature of the after-treatment device were below the light-off temperature. However, the CNG bus emitted a greater number of particles, mainly on the rural sector of the circuit. Finally, NOx and particle number concentrations along the route showed that traffic is a determining factor in creating areas with high concentrations of pollutants.

TTW (Tank to Wheel) and WTW (Well to Wheel) Analysis Using Electric Buses on the Line Eko 1 in Belgrade

The bus subsystem is the holder of the public transport function in many cities with a dominant representation of diesel-powered buses. In the last few years, electric buses (E-bus) have been increasingly used in many cities around the world (China, Europe, South America), making them the main alternative to conventional buses (diesel, CNG). The main advantages of using electric buses compared to conventional buses are higher energy efficiency, zero pollution emitted at the local level, more favorable carbon dioxide emissions observed at the regional or national level depending on the method of obtaining electricity, lower noise level. Since 2016, five electric buses have been operating in Belgrade on the EKO 1 line (Vukov spmenik-Belvil). The paper will present the environmental benefits of the use of electric buses observed through TTW (Tank to Wheel) and WTW (Well to Wheel) analysis, compared to diesel and CNG buses.

Total Cost of Ownership Analysis of the Impact of Vehicle Usage on the Economic Viability of Electric Vehicles in India

The road transport sector in India is on the cusp of a transition to battery electric vehicles (BEVs) from internal combustion engines (ICEs). Government of India (GoI) has announced several policy measures to push the adoption of electric vehicles (EVs). However, EVs involve a high capital cost but lower operating costs. Therefore, the economics of EVs vis-à-vis ICE vehicles depends on the extent of their daily use. The daily use, in turn, can vary significantly from context to context. In this paper, a model to compare the total cost of ownership (TCO) of an EV with different fuel variants (petrol, diesel, and compressed natural gas [CNG]) of their ICE counterparts is presented. It is found that, on an average, the TCO per km of electric two-wheelers (e-2Ws) and electric three-wheelers (e-3Ws) is less than their ICE counterparts at the typical average daily usage of the vehicles in Indian cities. In the case of hatchback and sedan cars, the TCO per km of electric cars (e-cars) is higher than their ICE counterparts. The TCO per km of electric bus (e-bus) is higher than diesel and CNG buses because of high initial purchase cost. Policymakers need to explore innovative business models and strategy for high vehicle utilization to improve the economic viability of EVs. Efficient planning of charging infrastructure and fast charging options will further help in accelerating the adoption of EVs in India.

Long short-term memory network-based emission models for conventional and new energy buses

Public transportation is regarded as a mitigation measure for addressing climate change and air quality deterioration. However, it is still necessary to estimate the emissions of transit buses, in particular when heavy loads and long periods of operation result in increased emission levels. Consequently, the primary objective of this study is to establish a method to estimate CO, CO2, HC, NOx emissions of buses with four different fuel types including gas-electric hybrid electric buses (GEHE buses), compressed natural gas buses (CNG buses), EURO 4 heavy-duty diesel engine buses (EURO 4 buses) and EURO 5 heavy-duty diesel engine buses (EURO 5 buses) based on the long short-term memory network. The proposed models can fully consider the time dependence of emissions response to vehicle operation situation. In addition, to evaluate the performance of the proposed models, an effective emission model which also addressed the time dependence of emissions by taking the elapsed time of acceleration and deceleration into account, was developed for emissions on each route for comparison. According to the estimation results, the emission models developed in this study performed better than the compared method in terms of emission rates and average emission factors, whose root mean squared errors (RMSE) were explicitly lower than the compared method, mean absolute percentile errors (MAPE) were lower than 50% of the compared method, and the predicted average emission factors were relatively more accurate than those of the compared models.

Study of the fuel efficiency and ecological aspects of CNG buses in urban public transport in Belgrade

Study of the fuel efficiency and ecological aspects of CNG buses in urban public transport in Belgrade

CNG 버스용 NGOC/LNT+SCR 촉매의 De-CH4/NOx 성능

CNG 버스용 NGOC/LNT+SCR 촉매의 De-CH4/NOx 성능

Estimation of bus emission models for different fuel types of buses under real conditions

Urban buses are heavy vehicles that move frequently throughout the day, and most of them are propelled by heavy-duty diesel engines. For these reasons, they have energy and environmental impacts that should not be ignored. Consequently, the primary objectives of this study were to compare the changes in bus speed, acceleration, and emissions between bus stops, intersections, and road sections by applying statistical methods; and to develop a vehicle specific power (VSP)-based artificial neural network (ANN) model to estimate emissions of CO, HC, NOX, and CO2 for four different fuel types of buses including gas-electric hybrid electric buses (GEHE bus), compressed natural gas buses (CNG bus), EURO 4 heavy-duty diesel engine buses (EURO 4 bus), and EURO 5 heavy-duty diesel engine buses (EURO 5 bus). The results of t-tests (with p-values varying between <0.001 and 0.026, which were not >0.050) showed that the differences in emissions between different locations and between different fuel types of buses were all statistically significant. In addition, to evaluate the performance of the proposed method, a polynomial regression model using linear, quadratic, and cubic terms of transient speed and acceleration was utilized for comparison. According to the results, the proposed method had more accurate and reliable estimation, which increased the lower 10% of absolute percentage error (Lower-10% APE) by 65.2%; reduced mean absolute percentage error (MAPE) by 41.4%, root mean squared error (RMSE) by 44.9%, and mean absolute error (MAE) by 43.5%; and increased R-squared from 0.659 to 0.781.