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TitleJaeheun Kim, Choongsik Bae and Hyundong Shin, “Fuel economy and emissions regarding valve events in engines”, The 2nd International Education Forum on Environment and Energy Science, Hungtington Beach, California, USA, Dec. 13-17, 2013.

Jaeheun Kim, Choongsik Bae and Hyundong Shin, “Fuel economy and emissions regarding valve events in engines”, The 2nd International Education Forum on Environment and Energy Science, Hungtington Beach, California, USA, Dec. 13-17, 2013.


Gasoline and diesel engines are the most widely used engines in the transportation sector. Each type of engine has their own advantages and disadvantages. They are still improving to meet with current stringent emissions and CO2 regulations.

Gasoline engines are widely used in passenger vehicles due to their cheap production cost and simple structure compared to diesel engines. However, the efficiency of the gasoline engines is lower than that of diesel engines due to lower compression ratio and higher pumping loss. The introduction of gasoline direct injection (GDI) and turbocharging technology has greatly improved the efficiency compared to the conventional port fuel injection (PFI) gasoline engines.

Several researches are also being conducted on varying valve events to reduce the pumping loss beside the technologies mentioned above. A novel camshaft design was proposed and the fuel efficiency was improved with flexible control of the camshaft duration [1]. The late intake valve closing (LIVC) strategy was an effective way to reduce the pumping loss for the gasoline engines in part load. These technologies have reduced the efficiency gap between gasoline and diesel engines.

Diesel engines are widely used in the commercial vehicles, heavy duty vehicles, ships and power plants. The diesel engines are very efficient due to their high compression ratio and lack of throttling loss. However, the hazardous emissions such as nitrogen oxides (NOx) and particulate matter (PM) are the major concern for the environment.

The research on the potentials of applying variable valve events on diesel engines, such as LIVC, are being conducted nowadays. The aim, however, is different from the gasoline engines. Since the pumping loss are not the major concern for the diesel engines, the target is to reduce the hazardous emissions with minimizing the fuel economy deterioration [2, 3].

The variable valvetrain would work in different manner in gasoline and diesel engines to achieve the different purposes. The objective is to compare the different valve event strategies that can possibly work on different engines. Additionally, their effects on the emission and engine performance were analyzed.

The experiment was conducted with the conditions shown in Table 1. The gasoline engine features continuous variable valve timing (CVVT) and continuous variable valve duration (CVVD) mechanism. Therefore the closing and opening of the intake and exhaust valve can be varied individually. Generally variable valvetrains such as CVVT or variable valve lift (VVL) are not in mass production for the diesel engines, due to limited clearance volume at top dead center (TDC) and lack of necessity to enhance the scavenging at part load condition. The intake valve closing (IVC) timing was varied only for the diesel engine to investigate the effects of reduced effective compression ratio on the fuel economy and emissions.

The in-cylinder pressure profile of two different engines were shown in Fig. 1. The pumping loss for the gasoline engine was higher than that of diesel engine. The LIVC strategies can effectively reduce the pumping loss of gasoline than that of diesel. Figure 2 shows the effect of LIVC strategies and oxygen concentration reduction on the NOx and smoke emissions in the diesel engine. The numbers in the legend indicate the crank angle degrees of retardation of IVC timing compared to the base value. It is known that the exhaust gas recirculation (EGR) is effective in reducing NOx emission. However, it can deteriorate smoke emission according to the NOx-smoke trade off relation due to lack of oxygen. The retardation of IVC timing was able to mitigate the smoke emission effectively while maintaining low NOx level. Figure 3 shows the effect of IVC timing and exhaust valve opening (EVO) timing on the brake specific fuel consumption (BSFC) in the gasoline engine. The BSFC can be minimized with the most retarded IVC timing with optimized EVO timing. The EVO timing determined the scavenging valve overlap duration, thus it should be optimized to achieve the best efficiency.

[1] J. Taylor, N Fraser, R. Dingelstadt and H. Hoffmann, Benefits of late inlet valve timing strategies afforded through the use of intake cam in cam applied to a gasoline turbocharge downsized engine, SAE 2011-01-0360
[2] X. He and R. P. Durrett, Late intake valve closing as an emission control strategy at Tier 2 Bin 5 Engine-Out NOx level, SAE 2008-01-0637
[3] J. Benajes, S. Molina, J. Martin, R. Novella, Effect of advancing the closing angle of the intake valves on diffusion-controlled combustion in a HD diesel engine, Applied Thermal Engineering 29 (2009) 1947-1954.


PreviousJoonsik Hwang, Donghoon Kim, Sangwook Han, Choongsik Bae, Jaewoong Hong and Sangyeon Shin, “Effects of the surface temperature and the coolang velocity on the erosion behavior of water jacket in a diesel engine”, International Conference on Multiphase Flow 2013, Jeju, Korea, May, 2013
NextDonghoon Kim and Choongsik Bae, “In-cylinder Characteristics of a Gasoline Direct Injection Compression Ignition Engine Using Computational Fluid Dynamics”, Acamedy for Co-creative Education of Environment and Energy Science (ACEEES), Perth, Australia, 2014
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