The Reality of Stop/Start Engines in Reducing Fuel Consumption
For many years, stop/start engines have been marketed as effective solutions for reducing fuel consumption. However, in reality, their impact is often limited and depends highly on driving conditions and specific engine designs. This article explores the effectiveness of stop/start engines and delves into the reasons behind their development and limitations.
Why Stop/Start Engines Were Developed
Stop/start systems, designed to reduce CO2 output in standardized government tests, have been a casualty of the automotive industry's need to meet stringent emissions standards. Fleet owners and car manufacturers benefit significantly from these systems, as they lower the tax bracket of vehicles, which can result in substantial financial gains.
For instance, in the UK, a slight difference in CO2 emissions—such as 121 grms per mile compared to 119 grms—can result in significant savings for car manufacturers, often in the millions of pounds. These systems also provide an opportunity to reduce idling time, which, though brief, significantly affects the CO2 output and, hence, the vehicle's class for taxation purposes.
How Stop/Start Systems Work
Stop/start systems, such as the E-Torque system in the Ram 1500, use a combination of a 40-volt electrical system, a belt-driven motor/generator, and a small battery. When the vehicle comes to a stop, the engine automatically shuts off. When the driver releases the brake, the belt-driven motor/generator starts the engine. This process eliminates the need for a conventional starter or alternator and uses a significant amount of torque for immediate acceleration.
The electrical motor also provides recovery through regenerative braking, which helps maintain battery levels and minimize energy usage, further contributing to the goal of reducing idling emissions.
Theoretical vs. Realistic Savings
The theoretical savings of these systems are significant, with claims stating that a 5.7L Hemi engine can save approximately 2 ounces of fuel while idling at a 90-second stoplight. Based on this, one gallon of fuel could potentially be saved for every 64 such stoplights. However, the reality is much different.
As a Ram 1500 owner with an E-Torque stop/start system, my experiences have not aligned with these expectations. Living in Phoenix, Arizona, where driving conditions predominantly involve long stretches of highway rather than urban or heavy traffic, the system has not saved as much fuel as expected. Additionally, cabin temperature can significantly affect the engagement of the stop/start system, with the air conditioning system continuing to run until the cabin is cooled to a comfortable level.
The Impact of Driving Conditions
The efficacy of stop/start engines depends largely on driving conditions. In areas with frequent stoplights, such as cities in rush hour traffic, the system can be highly beneficial. However, in regions with fewer stoplights, such as long stretches of highway, the savings are minimal.
Moreover, in hot climates like Phoenix, the air conditioning system’s continued operation can negate the potential fuel savings. This highlights the importance of understanding the specific conditions under which stop/start systems are most effective.
Conclusion
The reality of stop/start engines is that their effectiveness in reducing fuel consumption is highly dependent on driving conditions and the specific design of the system. While theoretically promising, practical results vary widely. Understanding these limitations and conditions is crucial for drivers and fleet owners to make informed decisions about the benefits of such systems.