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6. Hybrid bus demonstration: Société de transport de l'Outaouais and Société de transport de Montréal Gatineau and Montréal
7. Hybrid bus demonstration: Société de transport de l'Outaouais and Société de transport de Montréal Gatineau and Montréal

Hybrid bus demonstration: Société de transport de l'Outaouais and Société de transport de Montréal Gatineau and Montréal

Summary

Introduction

As part of Transport Canada's Urban Transportation Showcase Program, the STO (Outaouais transit corporation) and the STM (Montreal transit corporation) have developed a joint project comparing GHG emissions from hybrid diesel-electric buses and conventional diesel buses.

Methodology

The STM ran six conventional buses (Nova Bus's Nova LFS) and—on the same routes—eight buses of the same model and year equipped with a parallel EP40 hybrid electric system from Allison Transmission. The STO did likewise, using two hybrid buses and seven conventional ones.

In all, over 30 parameters were measured for one full year by a state-of-the-art data acquisition system that continuously measures and records data from the drive train as well as all aspects of the conditions under which the buses operate. Over 20 billion items of raw data were collected.

The comparison was based on three types of testing: during scheduled service, in the laboratory, and finally track tests.

For the scheduled service tests, routes in downtown Montreal were selected, as well as routes that go up and down hill near Mount Royal. Certain buses also travelled on routes in less densely built parts of the city. At Environment Canada's laboratories, fuel consumption and pollutant emissions were measured by examining the exhaust gases. There were 10 trials at the laboratories, at +20°C and at -20°C, and these also served to calibrate the data acquisition system.

STM's maintenance and engineering staff received one week's training on the hybrid buses. At the STO, all drivers received theoretical and practical training lasting 1¼ hours.

Results

Results are presented in terms of fuel consumption because GHG emissions are directly proportional to fuel consumption.

Scheduled service
On average, the buses under study travelled at 18 km/h and made 3.8 stops per kilometre. Temperatures ranged from -29oC to +33oC, with an average of 6.6oC. Under these conditions, fuel consumption was 65 litres per 100 km for the conventional buses, and 45 litres per 100 km for the hybrid buses, representing a saving of 30%. However when speeds reached around 100 km/h, both types of bus had very similar consumption levels. The study showed how the above general result varied with acceleration, speed, stopping frequency, air conditioning and temperature.

Rapid acceleration gives rise to greater fuel consumption than gentle acceleration—18% greater with hybrid buses and 42% greater with conventional buses. The figure is much lower with hybrids because a large portion of the energy required for acceleration comes from the energy recovered during the previous deceleration. Also, the power demand and rpm's of the diesel engine are controlled by the hybrid system's computer to optimize fuel consumption.

In a heavily congested area, at a mean speed of 10 km/h, the hybrids consumed 32 litres less per 100 km than conventional buses. At 30 km/h, the mean speed in the suburbs, the hybrids consumed about 11 litres less per 100 km.

The advantages of hybrids increased with the frequency of stopping. With one stop per kilometre, the hybrids consumed 16 litres less per 100 km than the conventional buses, but at 10 stops per kilometre, the difference rose to 24 litres.

At the STO, air conditioning increased consumption by 12% with the hybrids and by 17% with the conventional buses. However the air conditioning was on all the time, which is not representative of real conditions.

Between +15oC and -15oC, hybrids consumed 7 litres less per 100 km; about 3 litres of this difference was due to fuel consumption for heating.

Environment Canada laboratories
Engines compliant with the EPA 2007 standard do not emit particles or total hydrocarbons. The hybrid system emits 5% more nitrogen oxides (NOx) then the standard system.

There was a 36% decrease in consumption of fuel with the hybrid buses. For a bus that travels 70,000 km annually, that is equivalent to almost 36 tonnes per year, i.e. the equivalent of removing more than 7 vehicles from the road.

The outdoor temperature plays a role in the performance of the hybrid buses. At +20°C, the STM's hybrids consumed 37% less fuel than the conventional buses (62 vs 96 litres/100 km). Fuel consumption by the hybrids rises to 75 litres/100 km at -20°C. At the STO, the hybrids without air conditioning consumed 59 litres/100 km as compared to 73 litres/100 km consumed by the conventional buses, a difference of 19% in favour of the hybrids. The difference between the STM and STO results is due to the calibration of the engine/transmission duo on the STM buses.

Track tests
During the track tests, the degree of acceleration had much more impact on the conventional buses than on the hybrids.

Satisfaction surveys
Less noise and a smoother ride with hybrids are two benefits that may encourage people to switch from cars to public transit, leading to a significant reduction in GHGs.

The reactions of STM drivers to hybrid technology were positive: 92% felt at ease driving these vehicles. What they mainly appreciated was the reduced noise, followed by the smooth ride. Among bus riders, 63% found the ride quieter on the hybrids than on conventional buses, while 54% found it smoother.

Other technologies
The study also tested two other technologies which offer promising ways of reducing GHG emissions:

• Replacing hydraulic ventilation with  low-voltage electrical ventilation on both hybrid and conventional buses;
• Optimizing the transmissions on the conventional buses to give smoother acceleration, by replacing the existing control software with the Topodyn system.

At an average speed of 18 km/h including stops, the study found that:

• Electrical ventilation reduced fuel consumption by 16% (from 65 to 54 litres/100 km) on the conventional buses and by 22% (from 46 to 36 litres/100 km) on the hybrids.
• Use of the Topodyn control software reduced fuel consumption by 21% (from 65 to 51 litres/100 km) on the conventional buses.
• Combining both these technologies reduced fuel consumption by 31% on the conventional buses.
• The hybrids buses equipped with electrical ventilation saw a reduction in fuel consumption of about 20% (from 45 to 36 litres/100 km) when compared to the conventional buses equipped with both technologies.

Conclusion

The study has confirmed the claims in the literature about hybrid propulsion systems, namely that this technology is particularly beneficial with a fairly low average speed and frequent stops.

The analytical tools developed in the course of the study make it possible for the transit companies to foresee the impact of introducing hybrid buses on fuel consumption and hence on GHG emissions. To use the tables presented in this report, one only needs to know the average total speed and average total consumption¹. Any transit company can thus determine whether hybrids will be advantageous under its specific operating conditions.

To conclude, we may note that developments in hybrid technology will likely yield better performance in the years to come.

¹ The average total speed and the average total consumption are data available from the ECM of the Cummins engine.

Date modified:

2010-08-25

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