20/04/2017
Many car enthusiasts, particularly those new to the world of performance vehicles, often find themselves pondering the intricacies of different engine types. One such query that frequently arises is whether the legendary Mazda RX-7 is powered by a diesel engine. The short answer to this is a definitive no. The Mazda RX-7 is famously known for its groundbreaking rotary engine, a design that sets it apart from the vast majority of vehicles on the road today. This article aims to demystify the RX-7's powerplant, exploring what makes it unique, how it operates, and why it’s so revered among car aficionados.
The Rotary Revolution: What is it?
At its core, a rotary engine, often referred to as a Wankel engine after its inventor Felix Wankel, is an internal combustion engine that uses a triangular rotor instead of pistons. This rotor spins within a specially shaped housing, creating a series of chambers that perform the four-stroke cycle of intake, compression, combustion, and exhaust. Unlike a piston engine, which converts the linear (up-and-down) motion of pistons into rotational motion via a crankshaft, the Wankel engine's rotor directly produces rotational motion.
How Does a Rotary Engine Work?
The Wankel engine operates through three distinct phases occurring simultaneously as the rotor spins: 1. Intake: As the rotor turns, the space between one of its faces and the housing wall increases, creating a vacuum. This draws the air-fuel mixture into the combustion chamber. 2. Compression: As the rotor continues to rotate, the volume of this chamber decreases, compressing the air-fuel mixture. The apexes of the rotor maintain a seal against the housing's inner surface, ensuring effective compression. 3. Combustion (Power): Once compressed, a spark plug ignites the air-fuel mixture. The resulting explosion forces the rotor to continue its rotation, generating power. 4. Exhaust: As the rotor turns further, the chamber opens to an exhaust port, allowing the burnt gases to be expelled. This continuous, smooth rotation is a hallmark of rotary engines, leading to fewer vibrations and a more refined driving experience compared to many piston engines of similar displacement.
RX-7: A Rotary Icon
The Mazda RX-7, produced across three generations (SA/FB, FC, and FD), is perhaps the most famous and successful application of the Wankel rotary engine in a production car. Mazda's commitment to this engine technology was unwavering, with the RX-7 becoming synonymous with the unique performance characteristics that only a rotary can deliver. * First Generation (SA/FB, 1978-1985): Introduced with a naturally aspirated 1.1-litre 12A rotary engine, later generations saw the introduction of fuel injection and the more powerful 13B engine. * Second Generation (FC, 1985-1992): This generation featured both naturally aspirated and turbocharged versions of the 13B engine. The turbocharged models, in particular, offered exhilarating performance. * Third Generation (FD, 1992-2002): The FD RX-7 is the most iconic, featuring a sequential twin-turbocharged 13B-REW engine. This powerplant produced impressive horsepower for its displacement and was renowned for its smooth power delivery and high-revving nature.
Rotary vs. Piston Engines: A Comparison
To understand why the RX-7 is not a diesel and why its rotary engine is so special, it's helpful to compare it with a traditional piston engine.
| Feature | Rotary (Wankel) Engine | Piston Engine |
|---|---|---|
| Moving Parts | Rotor, eccentric shaft, stationary gears | Pistons, connecting rods, crankshaft, valves, camshafts |
| Motion | Direct rotational | Linear (reciprocating) converted to rotational |
| Size & Weight | More compact and lighter for equivalent power output | Larger and heavier for equivalent power output |
| Power Delivery | Smooth, less vibration, high-revving | Can be less smooth, more vibration, depends on design |
| Complexity | Mechanically simpler (fewer parts), but sealing is critical | More complex with many moving parts and valve train |
| Fuel Economy | Generally less efficient, higher fuel consumption | Generally more efficient, better fuel economy |
| Emissions | Can be more challenging to control, higher oil consumption | Generally easier to control, lower oil consumption |
| Torque | Often lower torque at lower RPMs | Can produce higher torque at lower RPMs |
| Maintenance | Apex seals require regular inspection/replacement | Regular oil changes, spark plugs, timing belt/chain |
Why Not Diesel?
Diesel engines operate on a different principle altogether. They use compression ignition, meaning the air-fuel mixture ignites solely due to the high temperature generated by extreme compression, without the need for spark plugs. Diesel fuel itself is also different, being less volatile than petrol (gasoline). The RX-7's rotary engine, like most petrol engines, relies on a spark plug to initiate combustion. Furthermore, the fundamental design and operating principles of a rotary engine are entirely incompatible with the high compression ratios and specific fuel requirements of a diesel engine.
Common Misconceptions and Considerations
Due to its unique nature, the rotary engine often faces misconceptions: * High Oil Consumption: Rotary engines do consume oil as part of their lubrication system, as oil is intentionally injected into the combustion chambers to lubricate the apex seals. This is normal but requires monitoring. * Apex Seal Wear: The apex seals, which are critical for maintaining compression, can wear over time and are a known maintenance item for rotary engines. Regular maintenance and proper driving techniques can prolong their life. * Fuel Economy: Historically, rotary engines have been less fuel-efficient than comparable piston engines, a trade-off for their compact size and smooth power delivery.
The Enduring Appeal
Despite these considerations, the Mazda RX-7 and its rotary engine hold a special place in automotive history. The unique sound, the incredibly smooth acceleration, and the compact, lightweight nature of the engine allowed Mazda to create a sports car with exceptional handling characteristics. The FD RX-7, in particular, with its twin-turbocharged 13B-REW, is a masterclass in engineering, offering a driving experience that few other cars can replicate.
Frequently Asked Questions
- Does the RX-7 use petrol or diesel fuel?The Mazda RX-7 exclusively uses petrol (gasoline) fuel. It is not compatible with diesel fuel.
- What makes a rotary engine different from a piston engine?A rotary engine uses a spinning triangular rotor within a specially shaped housing, while a piston engine uses reciprocating pistons moving up and down within cylinders.
- Is the rotary engine more powerful than a piston engine of the same size?Rotary engines are known for producing more power relative to their displacement and weight compared to piston engines, especially at higher RPMs.
- Are rotary engines reliable?When properly maintained and driven, rotary engines can be reliable. However, they require specific knowledge and attention, particularly regarding apex seals and oil levels. In conclusion, the Mazda RX-7 is a testament to innovative engineering, powered by a distinctive rotary engine that runs on petrol, not diesel. Its unique design offers a thrilling driving experience, cementing its status as an automotive icon.
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