Although HCCI combustion offers significant efficiency improvements compared to conventional spark ignition gasoline engines, traditional HCCI combustion can be realized only in a limited operating range. (Earlier post, earlier post.)

An HCCI engine ignites a mixture of fuel and air by compressing it in the cylinder. Unlike a spark ignition gas engine or diesel engine, HCCI produces a low-temperature, flameless release of energy throughout the entire combustion chamber.

To control the HCCI combustion process, the mixture composition and temperature must be changed in a complex and timely manner to achieve comparable performance of spark-ignition engines in the wide range of operating conditions. Achieving HCCI operation at low load is a challenge because the relatively low-temperature and light engine load characteristics generally inhibit the proper thermodynamic conditions for successful, controllable auto-ignition.

In this latest study by members of the team to enhance the effectiveness of a late fuel injection strategy in extending the low-load limit of HCCI engines, they used a numerical study to investigate the effects injection pressure and spray cone angle on the overall combustion efficiency and CO/NO_x emissions.

In general, they found that the in-cylinder charge stratification can be reduced by both an increased injection pressure and a wider spray cone angle, resulting in substantially lower NO_x emissions and reasonably high combustion efficiency simultaneously.

Resources

• SeungHwan Keum, Pinaki Pal, Hong G Im, Aristotelis Babjimopoulos, Dennis N Assanis (2015) “Effects of fuel injection parameters on the performance of homogeneous charge compression ignition at low-load conditions” International Journal of Engine Research doi: 10.1177/1468087415583597

• Keum, S., Im, H., and Assanis, D. (2009) “Computational Investigation of the Stratification Effects on DI/HCCI Engine Combustion at Low Load Conditions,” SAE Technical Paper 2009-01-2703 doi: 10.4271/2009-01-2703