*2.2. Purpose of the Work*

The purpose of this work was to evaluate the relationship between the indicated mean effective pressure of the fired cylinders (IMEPfrd) and the indicated mean effective pressure of the additional expansion cylinders (IMEPadd) of the tested engine, depending on the load and rotational speed of the engine. This approach allows us to estimate the load level below which the operation of the engine with the additional expansion of exhaust gases is not fully consistent with the main assumptions of such an engine, i.e., when an additional expansion process does not bring a positive effect. The results

of this research also allow us to assess the mechanical efficiency of the tested engine and to show how the effective efficiency of the engine changes in various test conditions.

### *2.3. Specific Features of the Test Engine*

As mentioned above, the basis for the development of the test engine was a mass-produced four-cylinder turbocharged spark-ignition engine. This engine is equipped with a gasoline direct injection system. The engine adaptation for this research was mainly focused on the modification of the cylinder head and camshaft. A different turbocharger dedicated to the engine with a smaller displacement was used. The control of the boost pressure was done through the wastegate valve integrated in the turbine housing. For the test engine, the exhaust and intake manifolds were designed and manufactured. The test engine is fully autonomous, which means that the power to drive the high-pressure fuel pump, alternator, water, and oil pumps is derived from the engine rather than from external sources. Basic technical data of the engine are summarized in Table 1.


An engine managemen<sup>t</sup> system (EMS) was built based on the stand alone AEM controller cooperating with the wide-band oxygen sensor. This EMS allowed us to change the operating parameters of the engine in real time during operation. High-pressure fuel injectors supplied with increased voltage were controlled using the Denso injector driver, because the EMS only allowed us to control high-resistance injectors.

Implementation of the engine concept presented in the scheme in Figure 2 required us to also develop modified camshafts, which provided valve timing as shown in Figure 4.

**Figure 4.** Valve timing of the test engine; Top Dead Center (TDC).
