Increasing Engine Efficiency of 4 Stroke
Methods to improve efficiency of fourstroke, spark ignition engines at part load
Abstract
The fourstroke, spark ignition (SI) engine pressure–volume diagram (p–V) contains two main parts. They are the compression–combustion–expansion (high pressure loop) and the exhaust-intake (low pressure or gas exchange loop) parts. The main reason for efficiency decrease at part load conditions for these types ofengines is the flow restriction at the cross sectional area of the intake system by partially closing the throttle valve, which leads to increased pumping losses and to increased low pressure loop area on the p–V diagram. Meanwhile, the poorer combustion quality, i.e. lower combustion speed and cycle to cycle variations, additionally influence these pressure loop areas. In this study, methods for increasingefficiency at part load conditions and their potential for practical use are investigated. The study also includes a review of the vast literature on the solution of this problem. This investigation shows that the potential for increasing theefficiency of SI engines at part load conditions is not yet exhausted. Each method has its own advantages and disadvantages. Among these, the most promising methods to decrease the fuel consumption at part load conditions are stratified charge and variable displacement engines. When used in combination, the other listed methods are more effective than their usage alone.
Keywords
- SI engine;
- Part load;
- Pumping loss;
- Efficiency;
- Fuel consumption
Figures and tables from this article:
- Fig. 1. Comparative pressure–volume (p–V) diagram of standard ideal Otto air cycle, ideal Otto fuel–air cycle and real engine cycle.
- Fig. 2. Schematic comparison of gross, pumping, net IMEP and their effect on indicated efficiency in high and low load conditions in SI engines.
- Fig. 3. (a) Thermodynamic model calculation results according to load conditions of a typical SI engine. (b) Pumping mean effective pressure to net indicated mean effective pressure ratio according to load and speed conditions of a typical SI engine [17].
- Fig. 5. Engine map of a typical SI engine with 4 cylinder 1600 cm3 stroke volume and road load of the vehicle (5. Speed)[19].
- Fig. 6. A comparison of real and calculated fuel consumptions at 50, 90 and 120 km/h constant speeds according to actual engine map and according to maximum engine overall effective efficiency of 34%.
- Fig. 7. Classification of some practical methods to increase the efficiency of SI engines at part load conditions.
- Fig. 8. Comparisons of load control with and without VVT and lift (early or late intake valve closing) on p–V diagram.
- Fig. 10. Comparison fuel consumption of a turbocharged and a naturally aspirated SI engine with similar maximum performance in the same vehicle [52].
- Fig. 11. (a) Thermodynamic model calculation results according to excess air coefficient and load condition of a SI engine. (b) Pressure rates of C3H8–air mixture in a constant volume chamber with different ignition timing delays (td) after fuel injection, which means different charge stratification. Injected fuel–air mixture is λ1 = 0.6 and overall mixture isλ = 1.25 [57].
- Fig. 12. Schematic comparison of a 2 cylinder SI engine p–V diagrams and corresponding efficiency without and with variable displacement at part load. Left side: 2 cylinders active. Throttle valve is nearly closed and pumping losses are high. Right side: 1 cylinder is cancelled and 1 cylinder is active. Throttle valve is more opened to get the same power and pumping losses are lower.
- Table 1. Comparison of the methods to decrease the fuel consumption of SI engines at part-load with the throttle controlled SI engine
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