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7. Truck Auxiliary Power Unit Field Trial

Truck Auxiliary Power Unit Field Trial

The analysis and conclusions contained in this case study are those of the authors alone and do not necessarily represent the point of view of the Government of Canada.

Organization
Mechron Power Systems

Major Findings
Using auxillary power units for 30 Class 8 trucks reduced fuel consmption by 2,400 L/truck/year and CO₂ emissions by 6.3 tonnes.

Project Timeline
June 2006 to March 2007

Please note that some figures such cost savings on fuel are based on data from the period that this project took place.

Introduction

It is well known that using main truck engines to meet cab heating and cooling needs during layovers is inefficient. Using small, efficient auxiliary power units (APUs) to provide cab comfort is a way to reduce fuel consumption and associated greenhouse gas (GHG) emissions. Mechron Power Systems began field trials using APUs in June 2006, and completed it in March 2007. This project was undertaken with financial assistance from Transport Canada’s Freight Sustainability Demonstration program.

Project Description

CCS Lightning trucks APUs (Figure 1 below) were installed in 30 Class 8 long haul trucks. Fuel consumption and GHG emissions data was monitored over nine months and compared to a control group of 30 similar trucks without APUs. Five control trucks were equipped with bunk heaters. The trial was conducted with the help of long haul fleets based in Ontario, operating on various routes throughout Canada and the United States. The fleet partners collected main engine data with engine control modules (ECMs) and provided access to APU-equipped trucks for data retrieval.

While control trucks were matched with APU-equipped trucks with similar routes, routes assigned to any particular truck can change with market conditions and general operational logistics such as driver turnover, vacations and truck repairs. In addition, APUs tended to be installed on newer trucks travelling longer routes. This means control trucks tended to have less idle opportunities than those with APUs. These small variances were not tracked. Twelve of the APU's were configured to allow warming the main engine before cold weather starting in addition to warming the cab and maintaining battery charge.

Project Goals and Objectives

The objective of this project was to conduct and document a field trial to assess the effectiveness of an APU to reduce GHG emissions and fuel consumption of Class 8 long-haul trucks by reducing main engine idling.

Project Methodology

Electronic control module (ECM) data from for all trucks compiled each month included:

• Drive time and distance travelled
• Average fuel consumption while not idling
• Average idle time per month
• Idle fuel per month
• Ratio of idle time to main engine time ratio

Every five minutes, the monitoring equipment installed in each of the 30 APU-equipped trucks sampled:

• Cab ambient temperature (^°C)
• Outside ambient temperature (^°C)
• APU output voltage (V)
• APU output current (amp.)
• Battery charger output voltage (V)
• Battery charger output current (amp.)
• Air conditioning (On/Off)
• Heater (On/Off)

APU data was also recorded for fuel use and run time in manual mode, fuel use and run and standby times in econo mode, and average APU fuel consumption rate. In econo mode, the APU runs only when there is power demand from the heating, ventilation and air conditioning (HVAC) unit. When the temperature inside the cab reaches the set point, the heat or air conditioning (A/C) turns off and the APU shuts down and restarts when there is a demand for heating or cooling. In normal mode, the APU runs continually. For either mode of operation, it is possible to activate the APU to warm the main engine with a timer if the APU is linked to the main engine cooling system.

A baseline test performed on a 2005 Cummins ISX450 engine determined fuel consumption rates at speeds between 650 and 1100 revolutions per minute (RPM). APU fuel consumption was determined by measuring the electrical power output using the data logging equipment and calculating the APU engine's fuel consumption required to deliver that power output. The function that correlates fuel consumption to output power was established through baseline testing of an APU under strict control of the electrical load. To determine APU exhaust emissions as a function of power output, Kubota Z482 emissions were obtained from its EPA 2005 Model Year Certificate of Conformity, issued April 14, 2004.

Initial data showed that many drivers did not operate the APU in econo mode, which is the most economical, especially in mild weather. Training and instructing drivers corrected this practice.

Five of the 30 control trucks had bunk heaters. Analysis compared the overall main engine idle time of these trucks to five other control trucks from the same fleet.

Results

Table 1 summarizes the project’s main findings. The results show that, on average, APU use reduced the fuel consumption of one long-haul truck by 1,820 litres over the summer-fall-winter study period. If it could be assumed that spring and fall conditions are similar, the annual fuel savings would be close to 2,400 litres. Since fuel consumption is directly linked to air emissions, APU use reduces pollutants such as particulates, NOx and non-methane hydrocarbon (NMHC) and about 6.3 tonnes of CO₂ emissions every year.

   Table 1 - Results

	Summer		FAll		Winter
	Truck	Truck w/APU	Truck	Truck w/APU	Truck	Truck w/APU
Truck in drive (averages)
Drive time (hrs/month)	244		208		160
Drive distance (km/month)	19,842		16,788		13,339
Drive fuel consumption (L/100 km)	41.92		41.09		38.89
Drive fuel (L/month)	8,317		6,898		5,188
Truck at idle (averages)
Idle fuel (L/month)	638.6	133.2	437.0	112.1	367.1	166.9
APU (averages)
APU run time (hrs/month)		118.6		116.9		157.0
APU fuel consumption (L/month)		117.8		135.7		170.5
APU fuel consumption rate (L/hr)		0.99		1.16		1.09
Portion of run time in Econo mode		66%		35%		59%
Consumption rate while in Manual mode		1.37		1.42		1.47
Consumption rate while in Econo mode		0.8		0.7		0.86
Summary
Total APU and idle fuel (L/month)	638.6	251.0	437.0	247.8	367.1	337.40
Total fuel (L/month)	8,955.6	8,568.0	7,335.0	7,145.8	5,555.1	5,525.40
Net fuel savings (L/month)	387.70		189.30		29.70
Net fuel savings (L/9 months)	1820.1
Total main engine run time (hrs./month)	354.3	267.0	309.4	234.0	240.5	196.6
Ratio of total idle time to main engine run time	45.2%	9.4%	48.8%	12.5%	50.3%	22.9%
Idle reduction time (hrs/month)	87.3		75.4		43.9
Idle time savings	24.6%		24.4%		18.3%
Total APU and idle CO2 (kg/month)	1,701.30	668.60	1,164.30	660.00	977.90	898.80
C02 reduction (tonnes/month)	1.033		0.504		0.079
C02 reduction (tonnes/9 months)	4.8

The averaged results showed lower fuel savings for winter than for summer. This may be because trucks travelling east-west routes in the winter log more idling or APU time due to the colder climate to pre-heat the main engine, and to maintain cab temperature. Trucks traveling north-south routes in the winter log lower idling/APU times because of a milder climate. In summer, both east-west and north south routes will need air conditioning. While the project results are not specific to travel routes, it can be concluded that on an annual basis, north-south trucking routes are likely to have shorter APU payback periods.

Five trucks were equipped with APUs able to warm the main engine before start up. Field data collected on these trucks compared reduction in idling time to the five control trucks without bunk heaters. The results showed a less than 2% difference in fuel use between control trucks with and trucks without bunk during layovers.

APU use is likely to reduce main engine wear but a cost benefit was not calculated in this project. The project did not track the level of thermal insulation in the trucks but it is known that improved insulation can further lower APU fuel use.

Conclusion

APUs are highly effective in reducing main engine idle fuel consumption while maintaining cab comfort. This project showed that they reduced fuel consumption by 2,400 L per truck per year with a resulting reduction of CO₂ emissions of 6.3 tonnes per year per truck.

Additional Information

• Mechron Power Systems

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Date modified:

2012-02-09

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