Is a smaller engine necessarily more efficient?

For several years, manufacturers have been reducing the capacity of their engines. They are downsizing. This is done to reduce emissions and comply with the latest standards. However, this strategy, supported by European governments, seems to be an utter failure.

In the automotive industry, downsizing refers to the reduction of engine displacement and/or the number of cylinders. This trend aims to reduce harmful emissions and energy consumption while maintaining or improving performance. However, several studies have shown that this strategy is a failure from an environmental point of view. In addition, some manufacturers have recently increased the engine capacity of their new models.

Why this strategy?

Emission calculation

To calculate the emissions and consumption of a vehicle, the WLTP cycle is used, which has replaced the NEDC cycle. These cycles include various tests to see if a vehicle meets pollution standards or not. This method includes driving at a constant speed, as well as idling. Smaller engines are more suited to this type of test.

Government

To reduce pollution and based on the cycles above, governments have promoted the use of small engines through laws and policies that provide incentives and punishments, including tax breaks and penalties. In particular, they have regularly lowered the number of grams of CO2 allowed per kilometre driven. Manufacturers have therefore had no choice but to take measures to make their vehicles follow the rules.

Why is it a failure?

NEDC and WLTP cycle

Several studies have shown that the NEDC and WLTP cycles do not correspond to the reality of car use. Thus, the real pollution values are quite different from those announced by manufacturers. In recent years, experts have noticed an increase in this discrepancy, which is reflected in the fact that true emissions are not dropping as expected.

Actual consumption

As mentioned above, the tests carried out are far from the actual conditions of use. Although efficient at constant low speeds, a small, low-powered engine will have to work harder to keep a vehicle moving at high speeds and under acceleration. It will need to rev up and downshift when overtaking or going uphill. A slightly larger engine with more torque tends to work less hard on such drives, allowing it to stay in a higher gear, which has a positive effect on fuel consumption.

Cost increase

To keep engines performing well despite a reduction in displacement, engineers have had to invent new technologies. Typically, they fitted turbochargers and added hybrid systems. All of this comes at a cost and creates mechanical complications that increase the purchase price and maintenance costs.

Reliability

Despite the reduction in engine size, cars have become larger and heavier. As a result, the energy required to accelerate a vehicle and then keep it at a constant speed has increased. As downsizing has not led to a loss of power, it has increased the usage intensity and, therefore, wear of components. The more power per ccm3, the greater the stresses. This raises several questions about the reliability and longevity of vehicles.

Downsizing has often led to increases in power, particularly through hybridisation. Again, this increases mechanical stress and complicates the power unit.

Conclusion

Downsizing has brought some improvements, particularly in terms of fuel consumption and efficiency. However, the tests carried out during the WLTP cycles are not representative of the real use of a vehicle. As a result, they favour small engines to such an extent that this becomes counterproductive. In real-world use, where accelerations and speeds are not constant, a relatively large engine can be more efficient than a smaller block. In addition, small displacement engines seem to suffer from unreliability due to high mechanical stress and technological complexity. To sum up, downsizing can make the car greener, as long as it is not pushed beyond reason.

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Sources - text

• https://realroadracing.com/engine-downsizing-the-good-and-the-bad/

• https://www.carkeys.co.uk/news/what-is-engine-downsizing-and-why-should-you-care

• https://www.carthrottle.com/post/car-makers-are-finally-admitting-that-downsizing-was-a-stupid-waste-of-time-and-money/

• https://www.evo.co.uk/features/18753/is-engine-downsizing-finally-falling-out-of-fashion

• https://www.hotcars.com/this-is-why-downsized-engines-have-been-disbanded/