Technology

Dedicated hybrid engines push engine efficiency beyond 45%

Thanks to Marc Sens of IAV for permission to use the chart from his talk, and to Reggie Zhan for contributions to this article

In the 2021 review paper on transport emissions, the section on gasoline engines started as follows:

“Current production engines show a best brake thermal efficiency (BTE) of around 41%, and to reach near-diesel efficiencies, gasoline engines must achieve 45% BTE. The development of dedicated hybrid engines (DHE) is now gaining increased attention, which allow optimization of engine efficiencies in a limited region and rely on the electric drive to
provide propulsion when the engine is traditionally inefficient.”

Only 3 years later, and against a backdrop of a surge in hybrid sales across the world, we are seeing OEMs announcing the commercialization of these engines. 

The chart below, taken from a recent keynote address by Marc Sens, Senior Vice President at IAV, summarizes the technology progression well.

 
References:
Joshi, A., “Review of Vehicle Engine Efficiency and Emissions,” SAE Technical Paper 2021-01-0575, 2021, doi:10.4271/2021-01-0575
Sens, M. Keynote talk at the CO2 Reduction for Transportation Systems Conference, Torino, 2024

What was being discussed as future potential has already made its way into commercially available engines. Here are a few examples from China, where extended-range plug-in hybrids are especially enjoying a rapid increase in market share. 

Geely Thor EM-i super electric hybrid engine

BTE = 46.5%

Fuel consumption 2.62 L/100km

Range 2,390 km

Displacement 1.5L, Pre-chamber, Miller cycle

Battery: 19 or 30 kWh

As shown in the picture, a engine with even higher BTE is being developed.

BYD DM Hybrid engine

BTE = 46.06%

 Fuel consumption 2.9L/100 km

Range 2,100 km

Displacement 1.5L, CR = 16.0:1,

Battery: BYD Blade LFP 10 or 16 kWh

Other

Dongfeng Mach hybrid PHREV : BTE = 45.18%, expect 48% in 2026

Changan Automobile Blue Whale hybrid engine BTE = 44.28%, reserve thermal efficiency can reach 47.03%

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