Engine performance can be improved by changing the valve opening (or closing) timing without any cam profile changes. In this study, a simple simulation model was created for valve timing misalignment, which is an assembly defect in the engine. Due to misalign, the opening angles of the valves have been changed between +20 degrees and −20 degrees compared to the normal opening angles. The engine performance resulting from this advanced and retarded valve timing was examined for a four-stroke, spark ignition, single-cylinder engine with an engine volume of 393 cc. In this study conducted for the 1000-7000 rpm engine speed range, first the in-cylinder pressure data were examined in detail and then the general engine performance parameters were examined. Accordingly, opening the valves earlier than necessary at low and medium engine speeds increases the maximum in-cylinder pressure, and at high engine speeds, it reduces the maximum in-cylinder pressure due to excessive decrease in volumetric efficiency. It was observed that the volumetric efficiency, which was 0.89 at medium speeds, decreased to 0.70 due to misalignment. Regardless of whether the misalignment is positive or negative, pressure fluctuations increase during the valve lapping process. Maximum braking torque occurs at medium engine speeds. Positive misalignment reduces braking torque, especially for low and high engine speeds. However, especially at high speeds, negative misalignment reduces the pumping torque. While the pumping torque for high engine speeds was −3.78 Nm, it increased up to −5.04 Nm due to positive misalignment. Whether it is positive misalignment or negative misalignment, brake specific fuel consumption tends to increase in both cases. At low and medium engine speeds, negative misalignment or positive misalignment always increases residual gas fraction. As a result of the study, it was seen that misalignment negatively affected engine performance. However, it is seen that the value accepted as reference is the optimum value for the operating speed range of the engine. With this study, it has been understood that valve timing, as well as valve system design, is vital for engine performance.

In this study, a simulation model with finite time thermodynamics was presented for an Otto cycle six-stroke engine. In this six-stroke engine, two free strokes occur after the exhaust stroke. These free strokes cause the engine to have higher thermal efficiency. Due to high thermal efficiency, these six-stroke engines can be used in hybrid electric vehicles. In this study, the effect of residual gas fraction and stroke ratio on the effective power and effective thermal efficiency were investigated. In addition, heat balance was obtained for the engine and the use of fuel energy in the engine was examined with the help of performance fractions. In the simulation model, the results are quite realistic as the working fluid was assumed to consist of fuel-air-residual gases mixture.

In this study, a dimensionless design approach was presented for translating flat-faced follower mechanism with two-circular-arc cam. Instead of second arc radius (r₂), maximum follower lift (s_max) and angle of the cam rotation angle (2θ_max) variables from the cam profile design parameters were made dimensionless using r₂∕r (=λ), s_max∕r (=ψ) and θ_max∕π (=μ) respectively. Equations for cam profile and follower movement were derived and graphics were obtained depending on the dimensionless parameters. λ and ψ should be in the range [0.0, 1.0], but μ should be in the range [0.0, 0.5]. λ and ψ were changed in the range [0.10, 0.90] and μ in the [0.25, 0.45] range and λ, ψ and μ values were determined for the cam profile. Maximum velocity (v_max), maximum absolute acceleration (a_max) and average follower lift (s_ave) changes, which are one of the critical characteristics of follower, were examined for possible cam profiles according to the change of λ, ψ and μ. As a result, v_max and s_ave decreased when μ was increased, v_max and s_ave increased and a_max decreased when ψ was increased, a_max and s_ave increased when λ was increased.