# Combustion and Emission Characteristics of a Biodiesel-Hydrogen Dual-Fuel Engine
## 2 Experimental Setup and Procedure
### Methodology  
During the research, part of biodiesel was replaced by hydrogen. To determine the maximum share of hydrogen delivered to the engine during the tests, the on-line observation of pressure curve, pressure increase rate, heat release rate and engine load in subsequent cycles was done. At the maximum hydrogen content, pre-ignition of hydrogen as well as pronounced knocking sound effects were observed during the tests. The tested engine managed to reach almost 40% of the energy share of hydrogen. During the tests, 200 engine cycles were recorded, and each measuring point was repeated at least three times. Before each measurement, the engine worked for several minutes to achieve thermal stabilization. Emissions of toxic exhaust gas components and soot were also recorded for each measuring point. Table 3 presents the energy shares of biodiesel and hydrogen for the analyzed cases. Because of the assumption of a constant load for the engine, the decrease in the biodiesel share was accompanied with an increase in the hydrogen share to achieve that assumption. Such shares as presented in Table 3 \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Biodiesel** & **Hydrogen** \\ \hline Molecular formula & \(\mathrm{CH_{3}}\)(CH\({}_{2}\))\({}_{n}\)COOH\({}_{3}\) & \(\mathrm{H_{2}}\) \\ Cetane number & 56 & 5–10 \\ Density at 1 atm and 15 \({}^{\circ}\)C (kg/m\({}^{3}\)) & 855 & 0.085 \\ Lower heating value (MJ/kg) & 37.1 & 119.81 \\ Heat of evaporation (kJ/kg) & 250 & - \\ Auto-ignition temperature (\({}^{\circ}\)C) & \(>\)101 & 585 \\ Flame speed, m/s & - & 2.65–3.25 \\ Stoichiometric air-fuel ratio & 12.5 & 34.3 \\ Viscosity at 40 \({}^{\circ}\)C (mPa\(\cdot\)s) & 4.51 & - \\ Boiling point (\({}^{\circ}\)C) & 180–360 & \(-\)2529 \\ Carbon content (\%) & 85 & 0 \\ Oxygen content, (\%) & 10.8 & 0 \\ Hydrogen content, (\%) & 12.1 & 100 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Fuel specification. resulted from measurements of biodiesel and hydrogen consumption and then were converted into energy shares. As it results from the data contained in Table 3 for tested engine, along with the increase of the hydrogen share in the fuel supplied to the engine, its energy demand decreases. Because of the hydrogen properties it should result in increase in engine thermal efficiency. The procedure for determining engine parameters and combustion stability evaluation is presented in the paper [4]. The indicated pressure is evaluated based on the recorded changes in the cylinder pressure and represents one of the indices that characterize operation of combustion engines in terms of the opportunities to ensure high and expected functional performance. Indicated mean effective pressure for a single engine cycle:  
\[\text{IMEP}_{\text{i}}=\frac{1}{\text{V}_{\text{d}}}\int\limits_{0}^{720} \text{pdV}\]  
where p is in-cylinder pressure, V is cylinder volume, V\({}_{\text{d}}\) is displaced cylinder volume. Indicated mean effective pressure:  
\[\text{IMEP}=\frac{\sum\limits_{\text{i=1}}^{\text{i=200}}\text{IMEP}_{\text{i}} }{200}\]  
where \"i\" is number of engine cycles. The thermal efficiency of the test engine:  
\[\text{TE}=\frac{\text{IMEP}\ \cdot\text{V}_{\text{d}}}{\text{Q}_{\text{B100}}+ \text{Q}_{\text{H2}}}100\%\]  
where IMEP is indicated mean effective pressure, V\({}_{\text{d}}\) is displaced cylinder volume, Q\({}_{\text{B100}}\) is the heat in biodiesel supplied to the cylinder and Q\({}_{\text{H2}}\) is the heat in hydrogen supplied to the intake manifold. Heat release rate (HRR) was calculated from the measured in-cylinder pressure data and crank angle readings. The basis of determining the heat release rate was the first law of thermodynamics and the equation of state.