Diesel Homogeneous Charge Compression Ignition (HCCI) combustion has several problems for practical application. One is the spray-wall impingement issue associated with early injection, and a further problem is the extension of HCCI operation from low loads to higher loads. In this study, a combination of Adaptive Injection Strategies (AIS) and Two-Stage Combustion (TSC) is proposed to solve the aforementioned problems for low emissions diesel operation.
AIS incorporates the use of multiple injections with different spray geometries and injection pressures. The basic idea of AIS is to use low-pressure narrow-angle sprays in early injections to prepare a homogeneous mixture for HCCI combustion, and to use conventional high-pressure wide-angle injections for conventional diesel diffusion combustion.
Using AIS, different combustion strategies can be realized under different engine operating conditions. HCCI combustion can be achieved at low load using low-pressure, narrow-angle injections. TSC is applied and optimized at medium load. Two combustion modes are combined in this concept. The first stage is ideally HCCI combustion and the second stage is diffusion combustion. AIS is used to achieve and optimize the TSC. The option of conventional diesel operation at high loads using high-pressure, wide-angle injections is still preserved and can be achieved using the proposed AIS concepts.
A multi-dimensional Computational Fluid Dynamics (CFD) code with detailed chemistry, the KIVA-CHEMKIN-GA code, was employed for the simulations, and Genetic Algorithms (GA) were used to optimize engine operating parameters. The simulation results showed that, using AIS with optimized engine operating parameters, a homogeneous mixture and HCCI combustion can be achieved with spray-wall impingement avoided. TSC can be realized by using AIS and can be applied to achieve low engine-out emissions at medium engine loads. The combination of the AIS and TSC concepts shows great potential to meet future ultra-low pollutant emission standards.