What are the benefits of using CGI instead of aluminium in a petrol engine? Shareholder, name withheld
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Materials selection for engine design is a vast and complicated subject, including technical, environmental, economical and even emotional considerations. It is therefore difficult to provide a simple answer to such a complicated question. Overall, the benefits of using CGI in a petrol engine are predominantly the same as in a diesel engine: package size; power; durability; well-to-wheels energy reduction; and, cost. The challenge, however, is that the peak firing pressure in petrol engines is lower than in diesels, so conventional grey cast iron and aluminium alloys can still offer sufficient durability for many applications. Many of the material decision factors are addressed in our engine design publication: Compacted Graphite Iron - A New Material for Highly Stressed Cylinder Blocks and Cylinder Heads
CGI is approximately 75% stronger, 50% stiffer and twice as durable as the aluminium alloys used for engine applications. These superior properties mean that engine designers can specify thinner walls in CGI, reducing the overall size of the cylinder block. In general, a CGI cylinder block could provide reductions of 10% in length, 5% in width and 5% in height in comparison to aluminium. This size reduction has many potential advantages, including (i) secondary weight savings because the components that span the length of the block (for example, cylinder heads, crankshafts, camshafts, fuel rails, etc) also become 10% shorter, and therefore lighter, (ii) easier packaging in the engine compartment, and (iii) less 'bridging' of front-end crash impact into the passenger compartment. This length advantage is more apparent in V-type engines, because V-engines benefit from the length and weight reductions on two cylinder banks.
As engine downsizing continues, and particularly as the use of turbocharging continues to increase, the mechanical load in petrol engines will increase. This can lead to a condition where stronger materials are needed to satisfy power, durability and package size requirements. If designers continue to use aluminium, the walls must become thicker, making the engine larger and heavier. This has already proven to be the case for V-diesel engines, where the Audi 3.0L V6 CGI diesel is 20% shorter and 8% lighter than the Mercedes 3.0L V6 diesel. It is therefore logical to assume that the initial CGI petrol applications will also be for V-type, turbocharged engines, due to the more challenging mechanical loads and the packaging benefits. In general, for engines where cylinder block durability is the rate-controlling-step, CGI petrol engines could be expected to provide approximately 20-30% more performance and approximately 100% more durability.
However, many non-technical factors influence in engine design. For example, if an OEM primarily uses aluminium for its existing petrol engines, it will take more effort, and competitive benchmarks from rival OEMs, to convert to CGI. This is because the casting, machining and assembly facilities are already in place for aluminium, and the competence of the design and manufacturing personnel are already aligned with aluminium. In such cases, a change of materials is a bigger and more expensive step. SinterCast must therefore concentrate its initial petrol efforts on the many OEMs that traditionally use iron.
Finally, economics and environmental considerations also influence materials decisions. In general, a CGI cylinder block will be approximately 50% less expensive than an aluminium cylinder block, and the well-to-wheels environmental profile of iron is more energy efficient than aluminium. It is true that a lighter engine can save fuel during the lifetime of the vehicle, but the energy required to produce aluminium is much higher than the energy required to produce iron. Indeed, it is not clear that the fuel savings provided by an aluminium engine over the life of the vehicle can payback the initial energy penalty. However, governments only regulate tailpipe emissions, with no regard for upstream energy consumption, and this motivates OEMs to prioritise vehicle weight over cost or life cycle energy efficiency. This is a frustrating oversight of legislators and SinterCast continues to educate and campaign for well-to-wheels accounting.
Engine designers will always prefer stronger materials, and this is the primary advantage for CGI. SinterCast has already announced that the first high volume CGI petrol engine has been approved for production and we believe that the launch of this engine will provide a new benchmark for performance, power-to-weight and energy efficiency. Our efforts to establish a first CGI reference in the petrol sector have been successful and we now look forward to the launch of this engine to increase the CGI awareness throughout the industry, establishing a new benchmark in the petrol sector, and providing further growth opportunities for SinterCast.