F2010-C-198 SIMULATION OF A SPARK IGNITION ENGINE WITH CYLINDERS DEACTIVATION 1Croitorescu, Valerian*, 1Maciac Andrei, 1Oprean Mircea, 1Andreescu Cristian 1Univeristy POLITEHNICA of Bucharest, Romania KEYWORDS - CO2 emissions, cylinder deactivation, simulation, fuel consumption, ICE ABSTRACT - During the next few years the automotive manufacturers will be ready to face the new engines providing the EURO 5 and EURO 6 demands. Many configurations of the internal combustion engines have been made with an aim to reduce the harmful gasses and CO2 emissions by decreasing the fuel consumption. The architecture of the propulsion systems and engines developed through many years considers both the spark ignition and diesel engines, combined with a conventional electric motor and a battery package. The hereby paper aims to create models and to simulate the operation of a propulsion system and an internal combustion engine, with 4 cylinders when two of the engine cylinders are deactivated trying to study the behavior of both the propulsion system and the engine in these cases. INTRODUCTION Hybrid vehicles are not the only answer to reduce harmful emissions and fuel consumption. The automotive manufacturers are developing an array of other promising technologies. To meet the requirement of decreasing emissions and fuel consumption they will have to enhance current internal combustion engine (ICE) technologies and develop some new ones. The variable displacement of the internal combustion engines by cylinder deactivation is one of them. Cylinder deactivation is part of a tool kit that the auto industry is using to improve fuel economy and reduce CO2 emissions. The technology helps the engine to seamlessly operate on a reduced number of cylinders under light conditions, such as when a vehicle is on the highway. By shutting off cylinders, the engine reduces fuel consumption while still retaining the flexibility to provide more power when necessary. The system allows the driver to operate on two, three or four cylinders, depending on driving conditions. For example, a driver can stay in two or three cylinder mode when driving along a highway with mild hills at speeds of up to about 130 km/h. The driver, as a result, gets more power without compromising the fuel consumption. At cruising speed, an ICE is working only at low percent of power and the throttle valve is only partially open, limiting the amount of fuel and air. This makes the engine work harder to draw air wasting power that could be used to propel the vehicle. Shutting down two of the four cylinders at cruising speed opens the throttle valve more fully, enabling the engine to breathe easier and reducing piston drag. MODEL AND SIMULATION PARAMETERS The variable displacement of the ICE will be simulated using the AMESim software tool. Developing the model for simulation consists in linking submodels from various software`s libraries. The submodels are shown as icons. After linking the icons (which represent each component of the vehicle) in sketch mode and choosing the proper submodel in submodel

mode, the parameters will be set. Each icon covers a fragment of C code, written using the specific equations for the system. In order to change the displacement of the ICE the cylinders was figured separately.

Figure 1: Model of the Gasoline Vehicle with Variable Displacement ICE

The submodel for the driver used in this model controls/calculates braking, acceleration and gear shifting. When the vehicle velocity is below a certain threshold, the neutral is engaged to avoid stalling. Acceleration and brake control take into account the anticipation of the speed control. The submodel for the ICE, which is a straight-four engine, computes the torque, the emissions, the fuel consumption, the exhaust gas flow rate and the consumption thermal losses. The ICE is controlled by an ECU which manages the different regulation modes and controls the torque request and computes the four following variables load requested by the driver, combustion mode, thermal coefficient combustion release, controlled idle speed. The ECU performs regulations for idle speed and maximum speed. The submodel for the 5 ratio gearbox includes the clutch and is controlled by the driver. The gearbox ratio is read in a data table. The primary shaft inertia and the powered axle are taken into account. The submodel for the vehicle models a simple vehicle load when considering no longitudinal slip between the tire and the ground. The configuration chosen for the vehicle is the roller test bench. The parameters used in the simulation are borrowed from an existing vehicle and are shown in Table 1.

Submodel Parameter Value / Unit

Engine

Type ICE-Spark Ignition Displacement 1997 cm3 Maximum power 110 kW / 5500 rev/min Maximum torque 180 Nm / 3750 rev/min Low threshold for engine temperature 20 degC High threshold for engine temperature 80 degC Hot engine idle speed 700 rev/min Cold engine idle speed 1100 rev/min Hot idle consumption 500 g/h Hot CO emissions 70 g/h Hot HC emissions 20 g/h Hot NOx emissions 0,7 g/h

Gearbox

Final drive gear ratio 4,13 Final drive efficiency 0,97 1st gear ratio 3,545 2nd gear ratio 1,913 3rd gear ratio 1,31 4th gear ratio 1,02 5th gear ratio 0,85 Gearbox efficiency 0,97

Vehicle

Kerb weight 1310 kg Wheel Inertia (4 wheels) 2,5 kgm2 Rolling radius 0,3 m Maximum brake torque 1000 Nm Drag coefficient 0,3 Frontal area 2,14 m2

Table 1: The parameters values used in simulation

SIMULATION AND RESULTS The simulation mode must follow the mission profile defined using tables and it will use the New European Driving Cycle (NEDC). The NEDC consists in the fact that the engine starts at 0 (zero) seconds and the emission sampling begins at the same time. The duration of the cycle is 1180 seconds. To verify if the model follows the NEDC the vehicle`s speed is compared with the control speed, as shown in figure 2. It can be observed that during all the 1180 seconds vehicle speed follows control speed given by the NEDC speed file.

Figure 2: Evolution of the vehicle speed and the control speed

The next steps it will evaluate the model with 2 cylinders deactivated as well as the model without deactivation on any cylinders. When 2 of the cylinders were deactivated it was considered that the load value was 60% of the maximum engine load. The evolutions of the engine torque follow each the normal curve (figure 3); only a few oscillations appear when the deactivated cylinders become active. The engine speed in both cases is the same (figure 4), no errors appeared. When two of the cylinders were deactivated the fuel consumption was lower by 15,43 % during the NEDC, as shown in figure 5 (a.532,7 g – b.629,9 g). Evaluation

of the engine torque variation with engine speed has shown that both engines function near economic pole, at a maximum of 3000 rev/min engine speed reaching the torque less than 150 Nm, as shown in figure 6.

a – Engine torque with 2 cylinders deactivated b – Engine torque without cylinder deactivation Figure 3: Evaluation of the engine torque

a – Engine speed with 2 cylinders deactivated b – Engine speed without cylinder deactivation Figure 4: Evaluation of the engine speed

a – Fuel consumption with 2 cylinders deactivated b – Engine speed without cylinder deactivation Figure 5: Evaluation of the fuel consumption

a – Engine torque with 2 cylinders deactivated b – Engine torque without cylinder deactivation Figure 6: Evaluation of the engine torque depending of the engine speed

By comparing the torque from one cylinder from the engine with deactivated cylinders with the torque from the same cylinder from the engine with non deactivated cylinders it can be observed that the first one (torque 1) develops more working points at high torque than the second one (torque 2).

a – Cylinders deactivated torque b – Cylinders non deactivated torque Figure 7: Evaluation of the cylinders torque depending of the engine speed

Figure 8: Evaluation of the cylinders torque during NEDC

Engine

load Fuel

consumption 0,1 596,461 0,2 578,284 0,3 565,825 0,4 557,978 0,5 541,907 0,6 532,696 0,7 529,133 0,8 522,177 0,9 516,663

Tabel 2: Fuel consumption values Figure 9: Fuel consumption at different values for EL

It is essential to know the evolution of the fuel consumption depending on the engine load when the cylinders are deactivated. Taking values from 10% to 90% of the maximum engine load for the moment when the cylinders will be deactivated (EL in figure 9) will result the dependence of the fuel consumption. CONCLUSIONS Cylinder deactivation is a good method to decrease fuel consumption and harmful emissions. Shutting down two of the four cylinders at cruising speed opens the throttle valve more fully, enabling the engine to "breathe" easier and reducing piston drag. The change in the number of "firing" cylinders is seamless. This can save as much as 18 percent of fuel, depending on the vehicle and the driver's habits. This method will compete with hybrid electric vehicles and fuel cells vehicles architectures, not to forget the alternative fuels technology which is also a great competitor in terms of fuel economy and low emissions. AKNOWLEDGMENT The present paper has been conducted within the framework of the `IDEI` contract, ID_1091/2007 and `POSDRU/6/1.5/s/19` contract, ID_7713/2007. REFERENCES (1) Oprean, I.M., “Automobilul modern (The modern automobile)”, Editura Academiei

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deactivation/index.html GLOSSARY ICE: internal combustion engine; ECU: electronic control unit NEDC: new European driving cycle