Development and experimental validation of a field programmable gate array–based in-cycle direct water injection control strategy for homogeneous charge compression ignition combustion stability

Abstract

Homogeneous charge compression ignition is a part-load combustion method, which can significantly reduce oxides of nitrogen (NO x) emissions compared to current lean-burn spark ignition engines. The challenge with homogeneous charge compression ignition combustion is the high cyclic variation due to the lack of direct ignition control. A fully variable electromagnetic valve train provides the internal exhaust gas recirculation through negative valve overlap which is required to obtain the necessary thermal energy to enable homogeneous charge compression ignition. This also increases the cyclic coupling as residual gas and unburnt fuel is transferred between cycles through exhaust gas recirculation. To improve combustion stability, an experimentally validated feed-forward water injection controller is presented. Utilizing the low latency and rapid calculation rate of a field programmable gate array, a real-time calculation of residual fuel mass is implemented on a prototyping engine controller. Using this field programmable gate array–based calculation, it is possible to calculate the amount of fuel and the required control interaction during an engine cycle. This controller prevents early rapid combustion following a late combustion cycle using direct water injection to cool the cylinder charge and counter the additional thermal energy from any residual fuel that is transferred between cycles. By cooling the trapped cylinder mass, the upcoming combustion phasing can be delayed to the desired setpoint. The controller was tested at several operating points and showed an improvement in the combustion stability as shown by a reduction in the standard deviation of combustion phasing and indicated mean effective pressure.

Homogeneous charge compression ignition combustion stability improvement using a rapid ignition system

“…Distinct cyclic variation in the corresponding combustion phasing C A 50 return map at operating point A. 28 …”

“…In previous work, the cyclic variation of HCCI has been reduced by preventing the early combustion following a misfire (cycle 3 in Figure 1) using direct water injection to cool the trapped exhaust gas to retard combustion phasing back to the desired value. 28–30 However, that leaves cycle 2 unaffected and the engine experiences a misfire leading to higher emissions and lower efficiency. The use of water injection adds the requirement for a second injection system and the requirement for a high quality water source for implementation in production vehicles.…”

Symposium for combustion control 2017 and 2018 special issue

“…Their work focused on closing the control loop by using ultra-fast field-programmable gate arrays (FPGAs) within a combustion cycle. 10,13 This extended the in-cycle control approach presented in the contribution of Liu et al 14 Another very important aspect of control development always lies on the process simulation. The contribution of Franken et al 9 presented a stochastic reactor model with tabulated chemistry.…”

“…The paper selection covers the main topics of the SCC, from advanced control concepts 2-4 to application-oriented papers with on-road vehicle validation 5,6 or detailed engine process control. [7][8][9][10] Innovative sensor and actuator technologies do not only enable greater flexibility in process control but also lead to greater complexity in future drive trains. For better knowledge of the system states, the concept of a ''soft-sensor'' gets a lot of attention, due to the possibility to reduce the hardware complexity and cost.…”

“…The intrinsic nonlinear behavior of the engine process was investigated by Nuss et al, 4 Sowman et al 3 and Ritter et al 12 by applying model predictive control approaches for the examples of selective catalytic reduction (SCR) aftertreatment and gasoline-controlled autoignition. Also, Gordon et al 10 and Wick et al 13 have investigated new control approaches for the homogeneous charge compression ignition (HCCI) process. Their work focused on closing the control loop by using ultra-fast field-programmable gate arrays (FPGAs) within a combustion cycle.…”