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The joy of carbs

6 months ago

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David Twohig | Engineer


19 January 2024

Fuel injection is amazing. Think about it. Petrol is a finicky old fuel. Too much air, and it won’t burn properly. Too little, and it won’t burn at all – that’s why you can chuck a lit match into a barrel of the stuff without it and you going up with a ‘woof’. [Disclaimer: don’t try this at home. Or anywhere else.]

You need 14.7 parts of air to each part of fuel to make it burn cleanly – a relation known as the stoichiometric ratio. Vary much either side of that mix and you either don’t get enough power, or you generate lots of nasty stuff – unburnt hydrocarbons, and various noxious oxides of carbon and nitrogen.

Fuel injection systems are capable of figuring this out on the fly. Their high-performance electronic brains are connected to the mass-airflow sensors that measure how much air is being sucked (or blown) into the engine, do the required mathematics at mind-boggling speed, and command ultra-precise injectors to squirt exactly the right amount of fuel into the intake to keep that engine at peak performance. All of this at any crank speed and any throttle opening, whether we’re under sea level in Death Valley at 50 deg C, or freezing our bits off 5882m (19,300ft) above it crossing the Umling La in the Indian Himalayas – claimed to be the world’s highest ‘road’.

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