Emir Yilmaz

With the decarbonization of internal combustion engines, alternative fuels have gained increasing attention. When using fuels with low combustibility, such as ammonia, detailed analysis of the intake system and in-cylinder flow is essential for improving combustion efficiency. Proper orthogonal decomposition (POD) has been widely used to extract coherent structures in flow fields within internal combustion engines. However, most previous studies have focused on analyzing cycle-to-cycle variations in gasoline engines, while time-resolved analysis within a single cycle of diesel engines has rarely been conducted. In this study, the effect of tangential port opening on in-cylinder flow characteristics was investigated using an optical single-cylinder diesel engine equipped with two intake ports and two exhaust ports. The opening area of the tangential port was varied under five conditions using different gaskets, and in-cylinder velocities were measured using particle image velocimetry. POD was applied to the acquired velocity data to evaluate the flow structures of the higher modes and their correlations with the mean flow and turbulence intensity. The results showed that in POD mode 1, a swirl flow was formed during the compression stroke when the tangential port opening exceeded 25%. Evaluation of the correlation between POD mode 1 and the ensemble-averaged flow using the relevance index revealed a strong correlation during the compression stroke. In POD mode 2, complex flows were observed during the intake stroke, and structures different from the mean flow were also confirmed during the compression stroke. A moderate correlation was observed between POD mode 2 and turbulence intensity under all conditions. Energy contribution analysis indicated that in the early intake stroke, the variation in mode 1 was large, and the flows represented by mode 2 and higher modes were dominant, whereas in the late compression stroke, mode 1 consistently accounted for a higher proportion.

Carbon dioxide (CO2) is the primary contributor to greenhouse gas emissions. Ammonia (NH3) has emerged as a promising alternative fuel due to its high energy density, ease of transportation, and carbon-free molecular structure. However, its practical application is challenged by slow combustion characteristics and high ignition temperatures. This study investigates the combustion behaviour of ethanol-ammonia mixtures using a high-compression-ratio engine (17.7:1) equipped with a sub-chamber. The engine operated at a constant speed of 1000 rpm. Ammonia energy ratios of 40%, 50%, and 60% were tested across ignition timings of 0°, 2°, 4°, 6°, and 8° crank angle (CA) before top dead center (BTDC). Results indicate that advancing the ignition timing increases in-cylinder pressure and heat release rate while reducing combustion duration. Lower ammonia energy ratios yielded higher thermal efficiency. Conversely, higher ammonia content and advanced ignition timings led to increased NOx emissions.

In the conventional map control, the number of calibration becomes large to make the map for transient driving conditions, which leads to extend the development period and increase the development cost. To overcome these shortcomings, the development of the model-based control is required. The previous model-based feedforward (FF) controller for diesel engines used several empirical equations based on experiments to predict the polytropic index for the compression stroke considering heat losses. To reduce the number of experiments, the authors developed the physical model for predicting the polytropic index (referred to as the present model) and implemented on the above FF controller. Under the transient driving conditions, it was found that the FF controller with the present model could predict the polytropic index with an average error of 0.31% and the indicated mean effective pressure (IMEP) with the maximum difference of 6.4 kPa, which shows that the present model can be used in place of the empirical equation.

For improvement of thermal efficiency of diesel engines, it is effective to control the fuel injection timing and quantity by using the model-based control (MBC) on ECU (on-board) with cycle-by-cycle calculation. The authors previouslydeveloped an on-board in-cylinder wall temperature prediction model and wall heat transfer prediction model those area part of models for MBC. The present study measured the time evolution of local wall temperature and heat flux in thecombustion chamber to evaluate the models. As a result of the wall temperature prediction model, it was made clear thatthe maximum error was 1.3% at the liner. About the wall heat transfer prediction model, it was shown that the maximumerror of heat flux was 5.8% at liner except for the inner head, and the average error of heat flux was -5.8% at the innerhead except for the cavity side wall.

Prediction of ignition timing through model-based control on ECU (on-board) is essential to improve the transient performance of diesel engines. In the previous studies, the authors developed an on-board polytropic index prediction model for compression stroke that was solely applicable under steady conditions. In the present study, newly developed models were added to improve prediction of the polytropic index for compression stroke under transient driving conditions. The average and maximum errors of polytropic index under transient conditions compared to the result of 1-D engine simulation were 0.37% and 1.06%, respectively. Additionally, the calculation time of the model per cycle was 50.6 μs, sufficient for on-board calculation.

<p> The present study conducted the derivation of the empirical equation in terms of the heat transfer phenomena at the intake manifold of internal combustion engines and the implementation of its equation to 1-D engine simulation. The derived equation allows to calculate the Nusselt number at the intake system, which causes to predict the mass flow rate of intake air into the cylinder accurately, ultimately improving the fuel consumption by controlling the auto-ignition timing. The empirical equation was developed based on the Colburn equation, taking into consideration of the effects of the thermal boundary layer development and the intermittent air flow induced by the opening and closing of intake valves. Compared with the experimental data, the average errors of the Colburn equation and the empirical equation were estimated to be 91.1% and 2.7%, which gives to improve the prediction accuracy of the Nusselt number by deriving the empirical equation. The equation was then implemented in 1-D engine simulation and compared to the results of the Colburn equation, revealing the maximum and average intake air temperature differences of 11.4 K and 2.7 K, respectively.</p>

The amount of air into IC engine's cylinders is affected by the heat transfer at the intake system, which is changed by the development of thermal boundary layer, the opening and closing of intake valve, and so forth. Our previous study developed the empirical equation for the intake manifold model assuming as the cycle-averaged quasi-steady state heat transfer. On the other hand, the present study also improved the newly empirical equation with the quasi-steady state heat transfer for the intake manifold of the actual IC engine. Consequently, the Nusselt number used in the newly empirical equation was expressed by using the Reynolds number, the Gratez number and the Strouhal number, which represents the effects of the intake air gas flow rate, the development of thermal boundary layer and the engine speed, respectively. In addition, the outlet air temperature at the intake port was estimated with the accuracy of maximum error of 5.6%, which was improved in comparison with the results obtained from the Colburn equation.