Freight Vehicle Improvement
Introduction
Being one of the major factors for growth in traffic volume, diesel trucks heavily contribute to air pollution, health impacts and climate change. Especially emerging economies are experiencing a large growth in freight volume and in the amount of diesel vehicles on the road. Considering China only, an increase in the amount of diesel vehicles from 10 million in 2005 to 60 million in 2035 is projected (World Bank), out of which trucks, buses and vans will continue to be the largest group. Despite known potential for improved fuel efficiency and emission reductions, the energy efficiency in the sector remains relatively low. This can partly be explained with the resistance of companies to experiment with new technologies, but also a lack of information regarding the availability and impacts of fuel efficient technologies is slowing down improvements.
Making diesel trucks more environmental friendly is an important task to sustain future transportation needs. This article deals with strategies to improve the vehicle body. However, it is important to apply a variety of strategies in order to maximize the energy efficiency. Eco-driving, enhanced maintenance and fuel improvements should - amongst other factors - also be taken into consideration.
Measures to Improve the Energy Efficiency
The main issues to be addressed can be summarized as aerodynamics optimization, weight reduction and a decrease of the tire resistance.
Aerodynamics
Certain points of a truck cause so-called aerodynamic drags. These can be found wherever there is a gap between two elements, such as the gap between the cab and the trailer, and between trailer and the road. Also the rear of the trailer pulls a drag behind, causing regions of turbulence. Scientific research has found that more than half of the energy consumed by a heavy vehicle driving at high speed is used to overcome aerodynamic drags, which means that the intensity of these drags largely influences the energy loss, and leads to a higher fuel consumption and emissions.
Nosecones
Nosecones are a common practice to assist the airflow from crosswinds and improve stability of the vehicle. The system bridges the gap between the tractor system and the trailer front wall and thus minimizes aerodynamic resistance through shaping. The reduction of turbulence can reduce fuel usage by approximately 3% when driving faster than 80kph (World Bank) compared to a truck without this aerodynamic improvement. Another advantage lies in the low investment costs.
Trailer Gaps
Trailer Gaps are another way to improve resistance from aerodynamics. Being installed between the back of the cab and the front of the trailer, the systems help to reduce the gap and lowers air turning downwards between the cab and the trailer, which would usually cause a change in air pressure and increases the total drag of the vehicle. Although this gap cannot completely be closed due to the need of space for turning, flexible materials can be installed as a compromise.
Trailer Skirts
Another aerodynamic improvement are trailer skirts. Bridging the air-drag causing gap between trailer and road, the skirts are mainly important for vehicles driving at a faster speed. Starting from approximately 75kph, the fuel savings through reduced wind under the trailer outweigh the extra weight which is being put on the vehicle through the skirts. Due to speed limits, traffic congestion, weather conditions, road quality and overloading, especially long-haul trucks in emerging and developing countries usually don’t reach this average speed, and thus the usage of trailer skirts should be carefully considered.
Weight Reduction
The weight of a vehicle has a direct influence on the amount of energy which is required to move it. Reducing the weight automatically leads to energy- and thus emission savings, and doesn’t compromise on performance factors of the vehicle. Especially aluminum offers the required characteristics which make it possible to replace heavy steel devices with the lighter material, saving up to 3.600 Euro on an empty big freight vehicle. Installing aluminum wheels and axle hubs is a common example, but even the trailer itself (walls and roof) has huge saving potentials. Another benefit of the lower weight is the opportunity to optimize the load of the vehicle. Due to legal regulations, trucks can only be loaded up to a certain limitation. Saving on the weight of the vehicle allows loading more freight, and especially for heavy goods such as steel or frozen goods, aluminum vehicles are more often used.
Tire Resistance
The amount of energy which is needed in order to get a tire moving, and to keep it moving, can be indicated as the tire resistance. Besides the quality of the tires, it also depends on the weight of the vehicle and the load. Having a longer lifespan than normal tires, low rolling resistance tires improve the truck stability due to the better quality and need less energy, which directly leads to cost and fuel savings. For heavy vehicles, a fuel reduction between 4% and 13% is realistic. Another 3% can be added by using single wide tires instead of double tires, which usually have approximately 20% less rolling resistance and weigh less. In order to keep the same tire pressure, monitoring systems and even automatic tire inflation systems can be installed on the truck respectively trailer. While the monitoring system still requires drivers to inflate the tires themselves, the automatic inflation system ensures a constant air pressure, which can increase the lifespan of the tires by up to 10% and decrease fuel usage by about 2%.
While specific fuel savings depend on various factors such as the vehicle size, weather conditions, road conditions and the driver, significant reductions in costs, fuel and emissions can be achieved in most cases. However, optimizing the fuel usage requires the application of other factors as well. More information can be found in the articles regarding Eco-Driving and Freight Vehicle Improvement.
Sources
http://www.ecostation.com/au/ReducingEmissions/FuelEfficiencyTechnologies/
http://ops.fhwa.dot.gov/publications/fhwahop10024/sect3.htm
Quick Guide to Truck Aerodynamics - http://www.freightbestpractice.org.uk/
The World Bank – Comprehensive Strategies to Reduce Diesel Emissions (Presentation by Paul Procee)
OECD (2011), Moving Freight with Better Trucks: Improving Safety, Productivity and Sustainability. OECD Publishing.http://dx.doi.org/10.1787/9789282102961-en
