KNOW THIS: Fuels
Alongside air, fuel is the essential ingredient to make your classic Ford’s engine run, we take a look at the many different types available.
Before we can understand how specific fuels will offer different benefits and advantages to our engine, we must first understand how our engine uses that fuel.There are two main types of internal combustion engine — spark ignition and compression ignition.
The term ‘spark ignition’ is what we would call a petrol engine — ‘compression ignition’ is what is more commonly known as a diesel engine. Although it may sound a little odd at first, these names actually give the biggest clue as to their main differences in the way they work.
Spark ignition engines have the compressed fuel/air mix ignited in the engine’s combustion chamber by spark plugs — which is why if you have dodgy spark plugs the engine won’t run properly.
Compression ignition engines, on the other hand, have the fuel/air mix ignited simply by being compressed inside the engine – which is why diesel engines don’t require spark plugs. Instead, they have to run very high static compression ratios and the fuel (diesel) is of a very low octane rating – allowing it to be ignited without a separate spark to initiate combustion. Another major difference worth noting is what effects altering the fuelling conditions will have — and they’re actually quite different.
Most of us will know that a petrol engine which runs too lean — especially when under load — can cause very hot running. This in turn leads to dangerously high exhaust gas temperatures, which can very quickly lead to severe engine damage. Therefore, many tuned cars will run deliberately rich to avoid these situations and aid reliability. However, as far as diesels are concerned, the leaner they run, the cooler they are. All diesel engines run incredibly lean in factory-spec (which is part of the reason why diesels are generally more fuel efficient than petrol).
They do this because increasing the air/fuel ratio to a richer mix causes the engine to produce the unsightly black smoke that diesels are known for.
To increase the power output of a diesel engine, we need to make the air/fuel mix richer. This is perfectly safe to some extent, but does need to be carefully controlled.The fact that lean-running isn’t a real problem, and there’s very little chance of the fuel/air mix pre-igniting before it’s required, means that diesel engines can run incredibly high boost pressures in comparison to spark ignition engines — some even exceed boost pressures well into three figures!