Detailed radiation modeling in piston engines has received relatively little attention to date. Recently, it is being revisited in light of current trends towards higher operating pressures and higher levels of exhaust-gas recirculation (EGR), both of which enhance molecular gas radiation. Advanced high-efficiency engines also are expected to function closer to the limits of stable operation, where even small perturbations to the energy balance can have a large influence on system behavior. Detailed radiation modeling using sophisticated tools like photon Monte Carlo/line-by-line (PMC/LBL) is computationally expensive. Here, guided by results from PMC/LBL, a simplified stepwise-gray spectral model in combination with a first-order spherical harmonics (P1 method) radiative transfer equation (RTE) solver is proposed and tested for engine-relevant conditions. Radiative emission, reabsorption and radiation reaching the walls are computed for a heavy-duty compression-ignition engine at part-load and full-load operating conditions with different levels of EGR and soot. The results are compared with those from PMC/LBL, P1/FSK (P1 with a full-spectrum k-distribution spectral model) and P1/Gray radiation models to assess the proposed model’s accuracy and computational cost. The results show that the proposed P1/StepwiseGray model can calculate reabsorption locally and globally with less than 10% error (with respect to PMC/LBL) at a small fraction of the computational cost of PMC/LBL (a factor of 30) and P1/FSK (a factor of 15). In contrast, error in computed reabsorption by the P1/Gray model is as high as 60%. It is expected that the simplified model should be broadly applicable to high-pressure hydrocarbon–air combustion systems, with or without soot.

迄今为止，活塞发动机中详细的辐射建模还很少受到关注。近来，根据当前趋向于更高的工作压力和更高水平的排气再循环（EGR）的趋势进行了重新研究，这两者都增强了分子气体的辐射。先进的高效率发动机也有望在稳定运行的极限附近发挥作用，在这种情况下，即使是很小的能量平衡扰动也会对系统行为产生很大影响。使用像光子蒙特卡洛/逐行（PMC / LBL）这样的复杂工具进行详细的辐射建模在计算上是昂贵的。在这里，以PMC / LBL的结果为指导，提出了与一阶球谐函数（P1方法）辐射传递方程（RTE）求解器组合的简化的逐步灰度光谱模型，并针对发动机相关条件进行了测试。对于重型压燃发动机，在部分负荷和满负荷工况下，使用不同水平的EGR和烟ot，计算了到达壁的辐射发射，再吸收和辐射。将结果与PMC / LBL，P1 / FSK（P1全光谱k-分布光谱模型）和P1 / Gray辐射模型，以评估所提出模型的准确性和计算成本。结果表明，提出的P1 / StepwiseGray模型可以局部和全局计算重吸收，且误差小于10％（相对于PMC / LBL），而PMC / LBL的计算成本仅为30倍，而P1 / FSK（系数为15）。相反，P1 / Gray模型在计算的重吸收中的误差高达60％。预计简化模型应广泛适用于有或没有烟灰的高压烃-空气燃烧系统。