We went to Le Mans a couple of weekends ago to see/watch/camp out at the 24hr race. We had lots of fun, plenty of beer and talked shite long into the night.
On Sunday morning we went to Arnage to watch the cars going round that corner and mostly talk more shite.
We talked about the different sounds the cars make and compared the noises made by the GT class Aston Martins and Corvettes as they slowed in the braking zone before the corner and then accelerated away after it. As you might expect there were lots of pops and bangs and back fires in the braking zone and a deep roar in the acceleration zone.
In contrast the LMP1 H cars make as sort of electric whirr as they braked and something similar as they accelerated away. Much less dramatic but very interesting.
These new sounds are the sound of efficiency. The hybrid drive systems on the LMP1 H cars are recovering kinetic energy during breaking and I think we're hearing the sound of electrical generators underload. In the acceleration zone that electrical energy is being release back in to the generators and using them as traction motors. Hence all the whirring.
What about the petrol and diesel engines in these cars I hear you ask? They've been silenced by further work to make them efficient as there are fuel consumption restrictions. The pops and bangs we heard from the GT cars was caused by un-burnt fuel burning in the exhaust system. I assume the GT cars have fuel injection systems that inject fuel into the intake manifold of each cylinder and not direct injection systems that inject fuel into the cylinders. This is an important difference because with manifold injection not quite all the fuel from each injection is sucked into the cylinder and burnt. This results in their being some fuel in the intake manifold. In the braking zone the drivers have lifted off the accelerator, the fuel supply is mostly cut off but there's still some fuel in the intake manifold. It the ECU has stopped firing the spark plugs then some of this fuel will make its way unburnt through the engine and into the exhaust where it explodes and makes great noises.
The hybrid cars with direct injection burn all the fuel that's injected in each cycle so there's no unburnt fuel to make the exciting noises. Also, some (all?) they hybrids are running turbos which further reduce the chances of backfires.
On Sunday morning we went to Arnage to watch the cars going round that corner and mostly talk more shite.
We talked about the different sounds the cars make and compared the noises made by the GT class Aston Martins and Corvettes as they slowed in the braking zone before the corner and then accelerated away after it. As you might expect there were lots of pops and bangs and back fires in the braking zone and a deep roar in the acceleration zone.
In contrast the LMP1 H cars make as sort of electric whirr as they braked and something similar as they accelerated away. Much less dramatic but very interesting.
These new sounds are the sound of efficiency. The hybrid drive systems on the LMP1 H cars are recovering kinetic energy during breaking and I think we're hearing the sound of electrical generators underload. In the acceleration zone that electrical energy is being release back in to the generators and using them as traction motors. Hence all the whirring.
What about the petrol and diesel engines in these cars I hear you ask? They've been silenced by further work to make them efficient as there are fuel consumption restrictions. The pops and bangs we heard from the GT cars was caused by un-burnt fuel burning in the exhaust system. I assume the GT cars have fuel injection systems that inject fuel into the intake manifold of each cylinder and not direct injection systems that inject fuel into the cylinders. This is an important difference because with manifold injection not quite all the fuel from each injection is sucked into the cylinder and burnt. This results in their being some fuel in the intake manifold. In the braking zone the drivers have lifted off the accelerator, the fuel supply is mostly cut off but there's still some fuel in the intake manifold. It the ECU has stopped firing the spark plugs then some of this fuel will make its way unburnt through the engine and into the exhaust where it explodes and makes great noises.
The hybrid cars with direct injection burn all the fuel that's injected in each cycle so there's no unburnt fuel to make the exciting noises. Also, some (all?) they hybrids are running turbos which further reduce the chances of backfires.
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