A hydraulic regenerative braking system for an articulated heavy vehicle is modelled for an idealised urban driving cycle, consisting of one stop and start from 30 mile/h, in a distance of 700 m. This model is used to guide specification of a hardware system but not to investigate brake blending methods or the torque distribution during braking. The specified system consists of a high-pressure accumulator and a low-pressure accumulator, connected by two fixed-displacement in-wheel pump–motors. One of these systems is fitted to each of the three trailer axles. This system can produce a fuel consumption saving of 21.7% over an idealised stop–start cycle. The same system was simulated over the Heavy Heavy-Duty Diesel Truck transient mode, New York City and Urban Driving Dynamometer Schedule legislative driving cycles, reducing fuel consumption by 11.2%, 17% and 11.7% respectively. Fuel consumption can be further reduced for all these cycles if engine stop–start technology is used. The potential to use the system when traversing hilly terrain was investigated, and the system was found to reduce fuel consumption by 12.6% over a V-shaped valley and by up to 5.3% over a realistic elevation profile.
One way to reduce the carbon dioxide emissions of heavy vehicles is to install regenerative braking systems. These capture the kinetic energy of the vehicle during braking and store it, in order to feed it back into the drivetrain during acceleration. It is not clear, however, which of the many available technologies should be used to implement this regenerative braking. This report explores the different possible energy capture and storage technologies for regenerative braking, including electrical, kinetic, hydraulic and compressed air. The basic systems are plotted on a selection chart, and an optimal selection methodology is used to aid in the selection of the lightest and smallest system for regenerative braking. The results of this comparison and selection show that hydraulic energy storage is likely to be 33% smaller and 20% lighter than the closest electrical counterparts and is therefore a logical selection for regenerative braking on the trailers of heavy goods vehicles.
Dual fuel diesel and natural gas heavy goods vehicles (HGVs) operate on a combination of the two fuels simultaneously. By substituting diesel for natural gas, vehicle operators can benefit from reduced fuel costs and as natural gas has a lower CO2 intensity compared to diesel, dual fuel HGVs have the potential to reduce greenhouse gas (GHG) emissions from the freight sector. In this study, energy consumption, greenhouse gas and noxious emissions for five after-market dual fuel configurations of two vehicle platforms are compared relative to their diesel-only baseline values over transient and steady state testing. Over a transient cycle, CO2 emissions are reduced by up to 9%; however, methane (CH4) emissions due to incomplete combustion lead to CO2e emissions that are 50-127% higher than the equivalent diesel vehicle. Oxidation catalysts evaluated on the vehicles at steady state reduced CH4 emissions by at most 15% at exhaust gas temperatures representative of transient conditions. This study highlights that control of CH4 emissions and improved control of in-cylinder CH4 combustion are required to reduce total GHG emissions of dual fuel HGVs relative to diesel vehicles.
The development, validation and control of a bi-mode train model is presented. A detailed modular model of a United Kingdom Class 800 train, which included carbon dioxide emissions data, was developed in MATLAB/Simulink. This model was validated against data obtained from a full day of rail journeys in the south-west of England. The validated model was used to develop control measures to reduce the carbon dioxide emissions of the train. Combining adaptive speed limit control with selective engine shutdown reduced the carbon dioxide emissions by 19.1% over a representative route without affecting the train’s on-time performance. The model was used to develop a tool for investigating the emissions benefits of (intermittent/discontinuous) route electrification. This tool shows that electrification of a route can reduce the carbon dioxide emissions by 66%.
A near-term strategy to reduce emissions from rail vehicles, as a path to full electrification for maximal decarbonisation, is to partially electrify a route, with the remainder of the route requiring an additional self-powered traction option. These rail vehicles are usually powered by a diesel engine when not operating on electrified track and are referred to as bi-mode vehicles. This paper analyses the benefits of discontinuous electrification compared to continuous electrification using the CO2 estimates from a validated high-fidelity bi-mode (diesel-electric) rail vehicle model. This analysis shows that 50% discontinuous electrification provides a maximum of 54% reduction in operational CO2 emissions when compared to the same length of continuously electrified track. The highest emissions savings occurred when leaving train stations where vehicles must accelerate quickly to line speed. These results were used to develop a linear regression model for fast estimation of CO2 emissions from diesel running and electrification benefits. This model was able to estimate the CO2 emissions from a route to within 10% of that given by the high-fidelity model. Finally, additional considerations such as cost and the embodied CO2 in electrification infrastructure were analysed to provide a comparison between continuous and discontinuous electrification. Discontinuous electrification can cost up to 56% less per reduction in lifetime emissions than continuous electrification and can save up to 2.3 times more lifetime CO2 per distance electrified.
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