A New Simple Function for Combustion and Cyclic Variation Modeling in Supercharged Spark Ignition Engines

Abstract

Research in the field of Internal Combustion (IC) engines focuses on the drastic reduction of both pollutant and greenhouse gas emissions. A promising alternative to gasoline and diesel fuel is represented by the use of gaseous fuels, above all green hydrogen but also Natural Gas (NG). In previous works, the authors investigated the performance, efficiency, and emissions of a supercharged Spark Ignition (SI) engine fueled with mixtures of gasoline and natural gas; a detailed research involving the combustion process of this kind of fuel mixture has been previously performed and a lot of experimental data have been collected. Combustion modeling is a fundamental tool in the design and optimization process of an IC engine. A simple way to simulate the combustion evolution is to implement a mathematical function that reproduces the mass fraction burned (MFB) profile; the most used for this purpose is the Wiebe function. In a previous work, the authors proposed an innovative mathematical model, the Hill function, that allowed a better interpolation of experimental MFB profiles when compared to the Wiebe function. In the research work presented here, both the traditional Wiebe and the innovative Hill function have been calibrated using experimental MFB profiles obtained from a supercharged SI engine fueled with mixtures of gasoline and natural gas in different proportions; the two calibrated functions have been implemented in a zero-dimensional (0-D) SI engine model and compared in terms of both Indicated Mean Effective Pressure (IMEP) and cyclic pressure variation prediction reliability. It was found that the Hill function allows a better IMEP prediction for all the operating conditions tested (several engine speeds, supercharging pressures, and fuel mixtures), with a maximum prediction error of 2.7% compared to 4.3% of the Wiebe function. A further analysis was also performed regarding the cyclic pressure variation that affects all the IC engines during combustion and may lead to irregular engine operation; in this case, the Hill function proved to better predict the cyclic pressure variation with respect to the Wiebe function.

On the Use of a Hydrogen-Fueled Engine in a Hybrid Electric Vehicle

“…A 0-D thermodynamic model, described in [22], properly calibrated using experimental data coming from a spark-ignition engine fueled with both gasoline and gaseous fuels [22,23], was used in the present work to obtain BTE maps of the engine when fueled with both gasoline and hydrogen. Table 1 shows the ICE specifications.…”

“…The above-described hybrid vehicle specifications correspond to that of a light duty passenger car [29]. The main differences between gasoline-and hydrogen-fueled engine simulations are that the gasoline engine is operated with a rich A/F mixture and limited SA near full load conditions (Figure 1) to avoid knocking phenomena, and this lowers the engine BTE compared to hydrogen configurations; and the combustion duration of a gasoline-fueled engine is set to around 80 CAD [16,22,23] while the hydrogen combustion duration is set to around 50 CAD (roughly 60% lower than gasoline as stated above), and this further increases the hydrogen engine BTE compared to gasoline operation.…”

“…The work proposed here starts from an existing spark-ignition ICE whose behavior, in terms of performance efficiency and pollutant emissions, has been widely explored experimentally both in gasoline and in natural gas (NG) operating modes [15][16][17][18][19][20][21]. The engine has been simulated with a zero-dimensional (0-D) thermodynamic model [22,23] that, after proper calibration with experimental data [22], is able to predict the engine performance in terms of BTE or Brake Specific Fuel Consumption (BSFC) maps.…”