Why Smaller Engine Vehicles are More Efficient
When it comes to the engines powering modern vehicles, sometimes the smaller the engine, the higher the efficiency. This article explores the reasons behind this phenomenon and explains why smaller vehicle engines often operate more efficiently than larger ones.
The Role of Throttle Position and Engine Efficiency
The efficiency of a petrol engine is closely linked to its throttle position. A petrol engine reaches its most efficient operating point when it is running at what we might call 'full throttle.' However, this is not the same as 'full power'. Efficiency peaks when the engine is at about 30% of full revs, a state known as 'throttle position'. At this point, the engine is operating closer to its optimal energy consumption and performance.
Why Smaller Engines are More Efficient
Smaller engine vehicles benefit from a fundamental principle of internal combustion engine operation: smaller engines can maintain their most efficient operating point more easily. When driving a smaller engine, you need to position the throttle further to maintain a certain speed. Conversely, with a larger engine, you have to throttle the engine more to achieve the same speed, thereby reducing the engine's efficiency.
Efficiency and Vehicle Load
Vehicle engines come in a variety of sizes, each designed to suit a specific type of task. On average, it takes no more than 22 horsepower (16 kilowatts) to propel an average-sized car at highway speeds on flat terrain. However, auto sales often emphasize the potential for maximum performance and acceleration, leading to the sale of larger engines. In reality, for most everyday driving, a smaller engine can be more efficient.
For instance, my first car, a VW Type 3 with a 1600 cc engine, could maintain about 85 mph on a tailwind, achieving an average fuel economy of 29 miles per gallon. While it struggled with steep highway grades and congested freeway on-ramps, it was a reliable five-passenger vehicle with a commendable fuel efficiency compared to larger American cars. With modern engine technology, even smaller engines can achieve similar or better performance, thanks to advancements like turbocharging, better cooling systems, and fuel injection.
The Shift to Electric Vehicles (EVs)
The advent of electric vehicles (EVs) introduces a new paradigm in vehicle efficiency. Unlike internal combustion engines (ICEs), EV motors exhibit better efficiency in larger sizes. The larger the motor, the better the regenerative braking system can work, capturing more energy during downhill driving and coasting to a stop and returning it to the battery. For ICEs, the idea of putting fuel back into the tank while coasting or descending is impractical, making larger engines inherently less efficient for most driving tasks.
Appropriate Engine Sizing for Commercial Vehicles
The concept of appropriate engine sizing is also evident in commercial vehicles like delivery vans and trucks. Just as a smaller engine car might be just right for its intended purpose, larger commercial vehicles can adopt engines that are perfectly suited for their tasks, without the added weight and inefficiency of oversized engines.
For example, a commercially suitable engine for a delivery van or truck might be sized to handle the car's load and do so with minimal energy loss. This approach not only enhances efficiency but also reduces wear and tear on the vehicle.
Conclusion
Efficiency in engine design is a complex but crucial aspect of modern automotive technology. While larger engines can offer impressive performance in certain scenarios, smaller engines often operate more efficiently, particularly in everyday driving scenarios. With the advent of electric vehicles and advancements in engine technology, the importance of appropriate engine sizing cannot be overstated. Smaller, more efficient engines are not only environmentally friendly but also cost-effective in the long run.
Understanding the principles of engine efficiency can help consumers make informed decisions when purchasing vehicles, ensuring they get the best performance for their needs and budget.