Mazda’s rotary engine in the age of the electric car

Why a rotary as a range extender?

• Rotary (Wankel) engines are compact with high power-to-weight and power-to-volume, attractive when space and mass are constrained.
• They naturally operate best in a narrow RPM band, which is a liability in conventional drivetrains but a good fit for a generator running at mostly constant speed.
• Mechanical simplicity, low vibration/noise/harshness, and brand identity for Mazda are repeatedly cited as motives.

Torque, efficiency, and emissions

• Low-end torque is generally described as a weakness of rotaries; this matters less when the unit only drives a generator.
• Rotaries have lower compression ratios and poor combustion-chamber geometry, hurting thermal efficiency compared with modern piston engines (especially high-compression, direct-injection Atkinson/Miller designs).
• Emissions are a major problem: effectively two‑stroke‑like oil consumption and long, moving combustion chambers make clean burn and fuel economy difficult. Side-port exhaust and direct injection improve things but don’t close the gap.

Reliability and apex seals

• Longstanding concern: apex seal wear, oil burning, and the need for rebuilds relatively early in vehicle life.
• Some argue modern seals and running at constant load/RPM could mitigate this; others say the basic geometry still limits compression and durability.
• Wankels are cited as a cautionary tale in engineering: an elegant core idea whose unsolved weak point (seals) dominates real-world viability.

Hybrid architectures and comparisons

• Thread contrasts series hybrids (engine only drives a generator) with parallel/powersplit systems (Prius, Honda, Volt).
• Consensus: series-only can be simpler but usually less efficient because of multiple conversion stages; mechanical coupling where possible is hard to beat.
• Prius-style Atkinson/Miller engines plus planetary gearsets are praised for real-world efficiency; MX‑30 R‑EV’s quoted fuel economy is notably worse than Prius and RAV4 plug‑in hybrids.
• Some see Mazda’s rotary use as technically interesting but inferior to conventional high-efficiency ICEs in this role.

Gas turbines and other alternatives

• Gas turbines are discussed as range extenders but are said to scale poorly to car-size power levels, with high cost and poor small-scale efficiency.
• Microturbines exist (including niche automotive concepts), but examples and data in the thread suggest high fuel consumption.

Hydrogen and future relevance

• Rotaries can reportedly run on hydrogen with limited changes, which some see as a future advantage.
• Others counter that burning hydrogen in cars is likely less efficient than using it to generate grid power for BEVs.

Market and user perspectives

• Some participants are enthusiastic about series hybrids/range extenders (Volt, BMW i3 REx, Mitsubishi Outlander PHEV), especially where charging is limited.
• Others, particularly from regions with dense charging infrastructure, see little point in ICE range extenders and expect pure EVs to dominate.