To improve the speed and accuracy of engine testing, the spark
(gasoline)/injection (diesel) timing can be optimized based on the
location of the 50% mass fraction burn point (α50) rather than the
traditional approach of "sweeping" timing to find the
most efficient point. Results from both gasoline and diesel engines
show that setting α50 to around 8° ATDC gives optimum efficiency
for most circumstances. An exception is the case of highly unstable
combustion, where the misfire rate may also be strongly dependent
on timing. For diesel engines this method is effective in finding
the timing for best efficiency but in practice the chosen injection
timing may be driven more by the need to optimize emissions.
This technique has been implemented by incorporating a burn
angle controller into the MAHLE Flexible ECU (MFE), a powerful and
highly adaptable engine controller. The MFE includes the burn angle
calculation (based on cylinder pressure signals) as well as the
main control strategy in a single robust unit, allowing for
straightforward test bed or vehicle operation of gasoline and
diesel engines. The burn angle controller also takes account of
knock and cylinder pressure limitations.
A high octane fuel demonstrator car was developed using the MFE
for the remapping of spark and other parameters. Optimum spark
timing was found by the burn angle controller while operating the
engine at different loads and speeds on a chassis dynamometer,
without needing to remove the engine from the vehicle. The remapped
engine delivered 15-20% more torque at low to medium speeds than
the baseline engine (at the same boost pressure), while reducing
fuel requirement due to lower exhaust temperatures. This could be
felt as much stronger vehicle performance and improved flexibility
in high gears.