Internal Combustion Engine: Effects of Cooling Intake Fuel on Power, Efficiency, and Emissions

Mechanical Engineering Laboratory (ME107)Spring 2016

University of California at Berkeley

Group 102-2

Gabriela GerinskaMatthew Charles Taul

Yanbo YaoGwen Gu

Amrita Srinivasan

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TABLE OF CONTENTS

1.0

ABSTRACT………………………………………………………………………………………….32.0

INTRODUCTION…………………………………………………………………………………...42.1 Equipment Background.

………………………………………………………………..42.2 Project Objective.……….

………………………………………………………………..42.3 Relevant Equations..…...

…………………………………………………………….....43.0 EXPERIMENTAL METHODS/DESIGNS...………………...…………………………………..5

3.1 Concept Generation.…....……………………………………………………………....5

3.2 Concept Selection.……..……………………………………………………….……….6

3.3 Build Process.…………………………………………………………………………….6

3.4 Data Selection.…………..……………………………………………………………….7

3.5 Data Collection………………..………………………………………………………….7

4.0 RESULTS & DISCUSSION………………………………………………………………….…...8

4.1 Results…………………….……………………………………………………………….9

4.2 Discussion……………….………………………………………………………………..9

4.3 Recommendation……….…………………………………………………….………..10

5.0

CONCLUSIONS…………………………………………………………………………………..106.0

REFERENCES……………………………………………………………………………….......117.0

APPENDIX………………………………………………………………………………………...117.1 Appendix A – Uncertainty

Analysis………………………………………………...117.2 Appendix B – Example Calculations ……………………………….

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7.3 Appendix C - Tables of Data Points Used in Plots……………………………...13

1.0 ABSTRACT

The objective of this project is to quantify the tradeoff between improved efficiency and increased total hydrocarbon emissions for an internal combustion engine when the fuel is cooled at the intake. We aim to determine if it is beneficial to run an engine on cooled fuel, where beneficial is defined as the ratio of power/exhaust gained by running on cooler fuel.

We expect to be able to generate more power from the engine by cooling the fuel. We expect this to occur because cooler fuel has a higher density, which would allow more fuel to enter every stroke, potentially allowing for a higher gain in power produced per stroke. However, we also expect that with this more fuel-rich mixture, more gasoline will also remained unburnt which will translate to an observable rise in T.HC (unburned hydrocarbons). Throughout this experiment we investigated how the ratio of power to T.HC changes when varying fuel intake temperatures and whether or not an increase in power will result in a proportional increase in T.HC levels.

We modified the mechanical system by isolating the intake fuel to be cooled, passing it through a fuel cooling device and then returning it to the engine’s fuel injector. The cooling bath was set at three different temperatures at which data was taken: -8°C, 0°C, 18°C. Baseline data was taken at ambient conditions of 20°C.

We parametrize our resulting power/ T.HC curves around varying RPM and throttle percentages. This allows us to describe the system in much greater detail and gives us the opportunity to see how the cooled fuel will affect the system with various secondary conditions in play.

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2.0 INTRODUCTION

2.1 Equipment Background

The equipment used in this project is a four cylinder 1986 Pontiac internal combustion (IC) engine with a capacity of 1.8 liters. The engine equipment also includes a Garrett turbocharger, Volvo intercooler, a catalytic converter, and an Eddy current dynamometer. The operational parameters of the engine are speed, ignition timing, and throttle percentage for controlling the amount of gasoline mixture entering the engine. By modifying these parameters, some changes in power output, flow rates, temperatures, torque, cylinder pressures, and exhaust gas compositions can be observed. The power output is equal to the speed times the torque. The exhaust gases includes some harmful emissions, namely, NOx, CO, and unburned hydrocarbons (T.HC). After exploring the operational parameters and observing the results of the initial measurements, we implemented some modifications on the intake fuel—namely, cooling it below ambient temperature—and then observing the effects that using cooled fuel has on engine performance.

2.2 Project Objective

Our project objective was to quantify the tradeoff between improved efficiency and increased total hydrocarbon emissions for an IC engine when the fuel is cooled at the intake. We aimed to determine the benefits of running an engine on cooled fuel, where beneficial is defined as the ratio of power output to exhaust. We expect increased power generation from the engine by cooling the fuel. Because cooler fuel has a higher density, more fuel can enter the engine on every stroke, potentially allowing for more power to be gained per stroke. However, we also expect that with a more fuel rich mixture, more gasoline will remained unconsumed, which would result in an observable rise in T.HC. If unburned fuel exhaust increases by 3% while output power rises by 5%, the trade off between an increase in unburned fuel will be balanced by the greater increase in power output. We want to investigate how the ratio of power/T.HC will change when varying temperatures of the intake fuel and whether or not an increase in power will result in a proportional increase in T.HC levels.

2.3 Relevant Equations

Engine power output:

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P = Speed∙Torque = v∙T = [rpm]×[N∙m]×2π60 ×[rad/sec] = [W] (1)

Power - T.HC concentration ratio:

P/CT .HC=2π60∙ v ∙TCT .HC

=¿ [W/ppmC](2)

3.0 EXPERIMENTAL METHODS/DESIGNS

In order to achieve our goal of cooling fuel, we aimed to design a fuel cooling device capable of quickly and efficiently cooling fuel. Additionally, we had to factor in the device’s ease of interfacing with and removal from the engine.

3.1 Concept Generation

We initially agreed upon several necessary components of the design, around which we built up several ideas. The fuel cooling device was to include copper tubing through which the gasoline would run; some type of cooling fluid in which the tubing was to be submerged; and a well-insulated container encasing the device.

● Dry Ice : One of our original ideas was to use dry ice to cool the fuel. The basic design would entail a container filled with dry ice in which the copper coil would be submerged. While dry ice is very good for cooling, handling could get quite complicated. Dry ice is usually at a temperature of -78.5°C so we would have to be careful in how we store it and not to come in direct contact with it. Furthermore, because dry ice gets so cold we might run into the issue of getting the fuel to be too cold which could alter the its properties.

● Coil & Cooler : This idea is quite simple with the design entailing a well insulated cooler, insulated copper tubing, and an ice bath in which the copper tubing was submerged. The copper tubing would be insulated to ensure that little heat was lost as the hot fuel runs through our cooling system. With this system we could reach ice bath temperatures as low as 0°C and with the addition of salt as low as -20°C.

● Coil & Pump : This design is the same as the coil and cooler design, but it also introduces a pump which would help with the mixing of the ice bath. The idea was that mixing would provide an even temperature distribution and allow for more even cooling due to forced convection.

● Multiple Coils & Cooler : This design is similar to the coil and cooler design, but it contains multiple coils and coolers. The coils would not be insulated, but because there would be multiple of them the fuel would have enough time to be cooled to the desired temperature.

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Fig.1 Dry Ice Sketch Fig. 2 Coil & Cooler Sketch

Fig.3 Coil & Pump Sketch Fig. 4 Multiplier Coil & Cooler

3.2 Concept Selection

We used a concept screening matrix to determine which of our design ideas we were going to implement. We decided to use the simple coil and cooler design based on the total score in the matrix.

Table 1: Concept Screening Matrix

3.3 Build Process

We first purchased a 30 gallon cooler wherein we could create an ice-water mixture. Inside the cooler 3-feet-long copper coil tubing was submerged. Two holes were drilled into the top of the cooler in order to allow the tubing to pass through. The two ends of the tubing were connected to the inlet and outlet of the fuel intake on the IC engine. To prevent the cooled fuel from heating as it traveled between the ice bath and the engine, the portion of the tubing exposed to ambient air

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was insulated with two types of insulation: fiberglass on the inside and foamed plastic on the outside. Finally, two holes were drilled on the side of the cooler to allow water to drain out upon completion of the experiments.

Fig. 5: Fuel Cooling Device Fig. 6: Device attaching to the engine

3.4 Selecting Data

Emissions and temperature data was collected at four different fuel temperatures. Data was collected at each temperature once with constant throttle (60%) and varied revolutions per minute (RPM), (2800 RPM, 3000 RPM, 3500 RPM, 3700 RPM, 4000 RPM) and once at constant RPM (2500) and varied throttle (30%, 45%, 60%, 75%, 90%). The four data points we decided to test were the following:

● Ambient air : This was our baseline “cooling” temperature, and it was used to compare results at all our subsequent data points. Data was taken at each parameter without our cooling device attached to the engine (i.e., normal engine setup). When baseline data was taken, the ambient air temperature measured between 20 and 23°C. Fuel was not cooled in these runs and so the temperature of the fuel at the intake was roughly the same as ambient.

● Cold water bath : The cooling device was attached to the engine in this case and the bath consisted of cold water. This temperature was selected as somewhat of a midpoint between our ice bath temperatures at ~1°C and the baseline temperature of ~20°C. The cold water bath was at 18°C and fuel was cooled to temperatures between 23 to 25 °C.

● Ice bath : The ice bath mixture was created using 19 liters of ice and 7 liters of water. The bath maintained a temperature of 1°C - 2°C. The fuel was cooled to temperatures between 4°C and 7°C. Higher mass flow rates associated with greater throttle percentages resulted in lower temperatures at the outlet of our cooling device.

● Salt water bath : The salt water bath was made using 26 liters of ice, 6 liters of water, and 750 g of salt for a 12% salt water mixture. The bath temperature was kept at -8°C and fuel was cooled to temperatures between 1.8°C and 4°C.

3.5 Data Collection

Torque, RPM, temperature, pressure, and emissions data were captured using LabVIEW VIs provided to us for this lab section. These VIs were written specifically to monitor and plot the sensor readings located in various positions on the engine test stand. There were other data sources, including fuel mass flow rate, fuel temperature before and after our test setup, and the cooling bath temperature, which were read into digital displays on the testing dashboard or digitally displayed in accessible locations. We ran the LabVIEW data collection scripts for

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approximately five minutes each once the engine had reached its steady state at a given test point. For temperature data which was read into digital displays, we recorded the values at the start, middle, and end of the testing period. Fuel mass flow rate was found by recording the total mass flow after a minute as timed with a stopwatch.

4.0 RESULTS & DISCUSSIONS

Using the latest data acquired from each experiment, we have created two plots showing the changes in the power/T.HC concentration ratio with respect to the intake fuel temperature (Fig. 7 & 8). Each point is presented with 95% confidence (see Appendix A for more details on the uncertainty calculations).

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Fig. 7 - Power-T.HC concentrations ratio over various temperature drops at 60% throttle (95% confidence)

Fig. 8 - Power/T.HC concentrations ratio over various temperature drops at 2500 rpm (95% confidence)

4.1 Results

As shown in Fig. 7 & 8, the power/T.HC concentration ratio does not increase or decrease monotonically as intake fuel temperature drops at both conditions tested - constant throttle and constant RPM.

At constant throttle of 60% and for an RPM of 3000, 3500, 3700, 4000, the power/T.HC ratio was low when the fuel was cooled by a cold water and salt ice bath. The ratio increased when the fuel was cooled by an ice bath. For 2800 RPM, the power/T.HC ratio increases as long as the fuel was cooled. The ratio increased the most when the fuel was cooled by an ice bath.

At constant RPM of 2500 and for 30% and 90% throttle, the power/T.HC ratio increased when the fuel was cooled by a water and ice bath. For 90% throttle, cooling the fuel with salted ice bath had no significant effects on the power/T.HC ratio. For 30% throttle, cooling the fuel with a salted ice bath decreased the ratio. For 45% and 60% throttle, cooling the fuel decreased the power/T.HC ratio. For 75% throttle, the ratio went up only when the fuel was cooled with an ice bath.

4.2 Discussion

Based on the results shown above, cooling the fuel with an ice bath appears to be the most beneficial. Cooling the fuel with an ice bath yielded an overall higher power/T.HC concentration ratio. The power/T.HC ratio is what we define as the measure of whether cooling the fuel was beneficial. A higher power/T.HC ratio means that there was a larger overall increase in power than there was an increase in T.HC emissions.

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At the occasion when cooling the fuel with an ice bath decreased the ratio, the drop of the ratio was small. Specifically, by cooling the fuel with an ice bath, the ratio was 1.08 to 10.33 times greater than the baseline data. For the cases where the ratio was lower than the baseline data, it was 0.18 to 3.36 smaller (see Appendix C for specific values).

As shown in Fig. 7 & 8, there were uncertainties in both the power/T.HC concentration ratio and the intake fuel temperature. The uncertainties for the power/T.HC ratio were obtained from equation 4. The uncertainties of the T.HC concentration, torque, and speed were obtained by applying the standard deviation function to the data taken and multiplying it by 2. We collected hundreds of data points for the T.HC concentration each run. Thus, it is appropriate to take the standard deviation directly and multiply it by 2 to obtain the uncertainty. For the intake fuel temperature, since only 2 or 3 data points each run were taken in each run, we used a t-distribution to determine the uncertainties for the temperature data (see Appendix A & B for more details on uncertainty analysis).

The T.HC concentration data contributed significantly to the uncertainties of the power/T.HC ratio because the T.HC concentration oscillates at some frequencies. This is reflected by the long error bars of the Power/T.HC ratio.

The uncertainties of the intake fuel temperature varied greatly because the intake fuel temperature was prone to variations throughout a run. When the uncertainties were zero (no horizontal error bars) there were no measured temperature variations throughout that run.

We noticed that the uncertainties tended to be largest at the beginning of a run, and tended to shrink in size to zero by the end of a run. We believe that this is a result in a cooling transient that persists in our system more at the beginning than end of a run. For instance, as the bath continues to cool the copper pipe at the beginning of our run, it is not removing as much heat from the intake fuel as it does later in the run when the pipe has reached an equilibrium temperature with the bath. This explains why the first set of data for each temperature set (whether 2800 rpm or 30% throttle) always ends up warmer than the following data points.

4.3 Recommendations

A natural extension of this experiment would be replicating some of the data points that we did not have time to repeat. Repeatability is an important factor of designing a good experiment. While we were able to successfully repeat some of our results we did not have time to repeat all results. Repeatable results would make our data stronger and would further support our conclusions.

Furthermore, we did not examine the effects that varying ignition timing would have on the system. We took some baseline data at ambient air temperature during which we varied ignition timing, but due to time constraints were not able to study the effects that differing temperatures and varying ignition timing have on the system.

Additionally, it would also be interesting to determine the exact temperature which optimizes the power/T.HC ratio. Based on our results the optimal temperature appears to be between 5°C and 8°C. Determining the exact temperature which optimizes the power/T.HC ratio would be a good conclusion for this experiment, but would require more precise cooling equipment than what was available to us.

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5.0 CONCLUSIONS

Cooling the fuel at the intake could be beneficial if the fuel is cooled to the right temperature. Form the results of our experiment, we it can be concluded that cooling the fuel with an ice bath was beneficial. However, lowering the bath temperature below 0°C by adding salt appeared not to optimize the ratio of power/T.HC as the ratio was lower than at ambient air.

6.0 REFERENCES

[1] Beckwith G. T., Lienhard V H. J., and Marangoni D. R., 2007, Mechanical Measurements, Pearson, MA, USA.

7.0 APPENDIX

7.1 Appendix A –Uncertainty analysis

Uncertainty in P/CT .HC [±% of the average P/CT .HC]:

uP /CT .HC

P /CT .HC=√❑

(3)

uP /CT .HC

P /CT .HC=√❑

(4)

where uv=2σv, uT=2σT , uCT .HC=2σCT . HC

Uncertainty in intake fuel temperature:

Sx=√❑(5)

μ= x̄ ± tα /2Sx /√❑ (6)

u❑intake fuel temp=t α /2S x/√❑ (7)

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For 95% confidence, α=0.05.t α /2 is read from the t-distribution table below:

Table 2a: Intake fuel temperature

Table 2b: Intake fuel temperature

Table 2c: Intake fuel temperature

Table 2d: Intake fuel temperature

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7.2 Appendix B - Example Calculations

Uncertainty in P/CT .HC at 2800 rpm and 60% throttle with ice water in the bath:uP /CT .HC

P /CT .HC=±√❑

uP /CT . HC=¿±4.71%×P /CT .HC❑=± 4.71%×28.95=±1.36 (vert. error bar)

Uncertainty in intake fuel temperature at 2800 rpm and 60% throttle with ice water in the bath:n=3Sx=√❑

u❑intake fuel temp=±t α /2Sx /√❑ (hori. error bar)μ= ¯6.27±0.1436.127≤μ≤6.413

7.3 Appendix C - Tables of Data points Used in Plots

Table 3: Values of P/T.HC and the corresponding fuel intake temperature with uncertainties at 60% throttle for various rpm values

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Table 4: Values of P/T.HC and the corresponding fuel intake temperature with uncertainties at 2500 rpm for various throttle percentages

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