Reducing the energy consumption and emissions of heavy goods vehicles using kinetic energy recovery systems

At our recent seminar Dr Daniel Ainalis of the Department of Civil and Environmental Engineering discussed his reasearch on minimising the impact of HGVs on our environment. Here he has kindly written us a complementary blog post on the topic. You can also download a PDF of his slides.

Climate change is one of the most pressing issues facing society today, with the Intergovernmental Panel on Climate Change recently calling for nations to make significant progress to limit global warming to 1.5°C above pre-industrial levels. The transport sector is a significant contributor to greenhouse gas emissions, accounting for 23% of these emissions in the UK.

HGVs, a global problem

A Heavy Goods Vehicles used to transport products around the United Kingdom.
Figure 1: A Heavy Goods Vehicles used to transport products around the United Kingdom.

Heavy Goods Vehicles (HGVs), which have a mass above 3.5 tonnes, alone contributed 16% of emissions from transport in the UK despite accounting for 5% of vehicle miles travelled. Transport is also a particularly challenging sector to decarbonise due to the current dependence on the use of oil as a fuel source. With global freight volumes predicted to increase 70% by 2030 according to the World Bank, there is an increasingly pressing need to decarbonise transport.

One solution to reduce greenhouse gas emissions is the electrification of transport, with technology advancing rapidly for passenger and light duty vehicles. It is, however, far more difficult to electrify HGVs, such as the ones shown in Figure 1, because of the the capacity and range requirements for these vehicles.

For exmaple the Tesla electric truck that was recently announced was stated to have a range of 800 km and consume 1.25 kWh/km. Considering that lithium-ion batteries have a specific energy of 0.1–0.265 kWh/kg, this results in a battery with a mass of 5–13 tonnes out of a maximum 44 tonnes for a HGV in the UK (not to mention the cost of the battery per kWh!). This would reduce the efficiency of high capacity HGVs and potentially their effectiveness: for example, a fleet operator may need to run an additional truck to compensate for the lower payload capacity.

Therefore, the electrification of HGVs is many years away from becoming commonplace, and in the short to medium-term other solutions need to be found to reduce their energy consumption and emissions. First, consider where energy losses occur for HGVs in urban drive cycles, illustrated in Figure 2.

The breakdown of energy losses of a Heavy Goods Vehicle operating in an urban drive cycle
Figure 2: The breakdown of energy losses of a Heavy Goods Vehicle operating in an urban drive cycle(by the energy delivered to the engine), from Review of the 21st Century Truck Partnership: 3rd Report.

Up to 50% of the energy provided to the engine for an HGV operating in urban areas is lost as heat during braking, highlighting the significant contribution of braking losses to vehicle inefficiency, greater than many factors including aerodynamic losses, rolling resistance, drivetrain losses, and auxiliary loads.

One approach that can be used to reduce the environmental impact and energy consumption of HGVs is through the use of a Kinetic Energy Recovery System (KERS), which recovers some of the energy normally lost during braking. A KERS has the potential to harvest braking energy during operation in urban areas increase HGV fuel efficiency by up 30%. Several options exist for recovering and storing the energy from regenerative braking systems, such as flywheels, hydraulics, and electrical storage systems.

KERS-URBAN Project

Our research project, KERS-URBAN, is funded by Innovate UK under the Low Emissions Freight and Logistics Trial. It aims to evaluate the technical and economic feasibility of a retrofitted KERS using ultra-capacitors as the storage for HGVs operating in urban areas. The project consortium involves two fleet operators Howdens Joinery Co., and Sainsbury’s Supermarkets, the technology provider Alternatech, and Imperial College London.

We are evaluating two different KERS architectures across three different HGVs in the trial. The first KERS architecture is fitted directly onto the drivetrain of the vehicle, while the second is installed onto the trailer. Photographs of the system installed on a trailer are shown in Figure 3.

Photographs of the retro-fitted kinetic energy recovery system: the motor/generator (left) and the ultra-capacitors with the electronic control unit and high-voltage modules (right).
Figure 3: Photographs of the retro-fitted kinetic energy recovery system: the motor/generator (left) and the ultra-capacitors with the electronic control unit and high-voltage modules (right).

Research Programme

The performance of 20 HGVs retrofitted with the KERS are being evaluated through a three-pronged approach involving:

  1. Real-world operational trials

The vehicles will continue to operate across a range of urban delivery routes and tracked using event-driven and time-resolved telematics data to track vehicle speed, distance, fuel consumption, and other key performance indicators. Control vehicles are also being simultaneously monitored to provide a relative comparison to the KERS HGVs in terms of fuel consumption and emissions reduction.

  1. Controlled fuel consumption and emissions tests

Controlled fuel and emissions tests will evaluate the KERS architectures and HGV configurations according to the protocol outlined by the Low Carbon Vehicle Partnership.

  1. Mathematical modelling of the HGVs and KERS architectures

The different vehicle and KERS architectures are modelled using ADVISOR (a simulation tool developed in Matlab/Simulink to evaluate the fuel efficiency, emissions, and performance of hybrid powertrain vehicles). The data acquired from the operational trials and controlled tests will be used to validate the HGV-KERS models. Once validated, these models will be used as a tool to predict the performance of the different vehicles and KERS architectures for a variety of different operations.

The programme is expected to provide the following outputs related to the feasibility of KERS for low emissions transport in HGVs:

  1. The fuel savings, emissions and noise reduction of each KERS architecture will be quantified for all deployed units over a range of drive cycles, loads, and weather conditions.
  2. Empirical models of the geometries under study will be used to optimise driving styles and routes to minimise fuel consumption, GHG and air pollutant emissions.
  3. Model validation will result in a tool that can predict the performance of different KERS architectures over a variety of different vehicles and operations. This validated model will be used with a HGV fleet mix optimisation algorithm to determine optimal solutions for a variety of applications minimising fuel consumption, emissions, and system costs.

At the end of the trial, the thorough evaluation of the economic and technical feasibility will be leveraged by fleet operators and vehicle manufacturers to make an informed decision about the implementation of an ultra-capacitor based KERS for HGVs operating in urban areas to reduce fuel consumption and emissions.

Biography

Dr Daniel Ainalis Dr Daniel Ainalis is a Research Associate in the Centre for Transport Studies at Imperial College London and works across both the Transport & Environment Laboratory and the Transport Systems & Logistics Laboratory on alternative vehicle technologies and strategies to reduce energy consumption and emissions.

Daniel has expertise in vehicle dynamics, vehicle telematics acquisition and analysis, road roughness measurement, analysis and simulation, signal processing, and mechanical vibrations. He obtained his Ph.D. at Victoria University in Melbourne, Australia, in the areas of vehicle dynamics and distribution vibrations.

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