There are nevertheless challenges with this approach, particularly combustion knock
which increases with compression ratio .
That usually meant intake air and the intake manifold had to be heated to improve vaporization, the combustion chamber had to be carefully designed and kept clean to prevent knock, and for some engines (Rumely OilPull and the early John Deere D, for instance) water was injected into the cylinders to moderate combustion so as to further prevent combustion knock. These engines do not "bum" water, as some people think.
Lower compression than with gasoline is required to prevent combustion knock and potential engine damage.
The LucasVarity common rail system also includes several optional features, including absolute torque control using a speed signal and the use of an accelerometer for monitoring of combustion knock.
An accelerometer can be fitted to the engine block to monitor combustion knock. The sensor signal is passed through an additional hardware chip, and the software processes the signal.
During the first half of this century, there was a major focus on avoiding combustion knock
, which was blocking the route to increased efficiency and specific power.
[29.] Szwaja, S., Bhandary, K, and Naber J., "Comparisons of hydrogen and gasoline combustion knock
in a spark ignition engine," Int.
(6.) Szwaja S., Bhandary, K.R., Naber, J.D., Comparisons of hydrogen and gasoline combustion knock
in a spark ignition engine, Int J Hydrogen Energy, 32: 5076-5087,2007
[15.] Dues, S., Adams, J., and Shinkle, G., "Combustion Knock
Sensing: Sensor Selection and Application Issues," SAE Technical Paper 900488, 1990, doi:10.4271/900488.