A Novel Dual-Electrode Plug to Achieve Intensive Electric Field for High Performance Ignition

Abstract

A thorough analysis of electric field is carried out so as to verify that a novel dual-electrode plug can build intensive electric field and can improve the main drawbacks of feeble electric field and low ignition efficiency of the traditional plug. With intensive electric field, the proposed novel plug can achieve high performance ignition, resulting in fuel saving and exhaust reduction. Gauss law is applied for electric field analysis to show that intensive electric field can be built by the novel plug. Then, according to Faraday law a lower-voltage ignition feature accomplished by the plug is discussed. Compared with traditional plug, the novel dual-electrode plug has the following advantages. (1) Much higher energy density is built between the plug electrodes, lowering ignition voltage requirement. (2) Electromagnetic interference (EMI) problem caused by high ignition voltage is readily resolved. (3) Ignition time delay can be improved. (4) The feature to save fuel consuming is achieved. (5) The exhaust of CO and HC is reduced significantly. Practical measurements are fulfilled to validate the electric field analysis and to demonstrate the features of the proposed dual-electrode plug.

1. Introduction

Recently, the world is facing the threat of global warming due to the heavy use of fossil fuels and other greenhouse gases which result in a substantial increase of carbon dioxide. There are 24% of carbon dioxide emissions across the world, which is produced by the transportation tools. Mostly, it is produced from motor vehicles because of the use of fossil fuel [1]. In order to reduce the emission pollution from transportation tools, one has to understand how an electrical field is built by the spark plug and how a time delay is caused by the spark plug. In general, the operation of a vehicle engine can be divided into four steps: (1) intake, (2) compression, (3) explosive combustion, and (4) exhaust.

In an engine ignition cycle [2, 3], the engine power comes from which the explosion of the spark plug ignites the compressed mixed gas, and then the piston pushes the crankshaft rotation to generate power output. When the cross-section of the electrodes of the spark plug is too large, the spark arc will not concentrate at a point easily. Thus, this is difficult to start the engine and is prone to cause an incomplete combustion, resulting in exhaust pollution. Moreover, it needs a higher ignition voltage to produce a critical electrical field for the plug. A higher ignition voltage will cause a more serious EMI problem. Besides, if a plug needs a high ignition voltage, it has to take longer time for voltage accumulation, leading to time delay for igniting. Figure 1 illustrates that an optimal igniting time locates at the 10 degrees of crankshaft.

Figure 1 

The relationship between crankshaft position and the combustion chamber pressure.

Therefore, the establishment of the ignition voltage and electric field [4–6] for a spark plug is very important. In this paper, with the application of Maxwell equations [7, 8], we propose a dual-electrode enhanced electric field plug for combustion engines. The proposed plug not only can build a more intensive ignition electric field and can produce a spark arc in time.

2. The Proposed Plug Structure

To ignite the proposed spark plug, a corresponding block diagram of the ignition system is shown in Figure 2, in which the DC/DC converter can be implemented by a switch-mode converter [9–15]. In this paper, the flyback-type converter is adopted to fulfill high voltage generation. In the following, we will deal with the electric field analysis and ignition voltage discussion.

Figure 2 

A block diagram of electronic ignition system.

2.1. Principle of Dual-Electrode Plug with Enhanced Electric Field

Figure 3 illustrates the structure of the output of an ignition system. According to Ampere theorem, one can know that charges will flow to the spark plug electrodes and then build an electrical field. When the electric field between the spark plug electrodes reaches the critical electrical field 𝐸_𝐶, charges release energy and produce arc sparkle to ignite mixed gas for generating power [16]. In addition, the current and output charge of a high voltage ignition coil at each ignition time interval can be expressed as follows: Δ𝑞=𝑖(𝑡)Δ𝑡, (1) where Δ𝑞 is the total charge supplied to the plug.

Figure 3 

A simplified diagram to express the structure of the output of the ignition system.

2.2. Critical Electric Field Built by Traditional Plug

Figure 4 shows the structure of a traditional spark plug, in which a Gaussian cylindrical shell is selected. The positive electrode is placed at the middle of the spark plug electrodes. In Figure 4, 𝐴₁ is the cross-section of the positive electrode, 𝑉_𝑖 is the voltage of the positive electrode, 𝑉_𝑓 is the voltage of the negative electrode, 𝑑 is the distance between the plug electrodes, and −Δ𝑞 is the induced charge by +Δ𝑞. A critical electric field, 𝐸_𝐶, is calculated as follows: 𝜀₀𝐸⋅𝑑𝐴=𝑞, (2) where  𝜀₀ is the permittivity of free space. The critical electrical field 𝐸_𝐶 established between the two electrodes is 𝐸_𝐶=Δ𝑞𝜀₀𝐴₁. (3)

Figure 4 

The structure of the traditional spark plug.

From Faraday law, one can obtain 𝐸⋅𝑑𝑠⃗=−𝑑Φ_𝐵𝑑𝑡=−𝑉. (4)

The ignition voltage established between the two electrodes is 𝐸_𝐶⋅𝑑𝑠⃗=𝐸_𝐶𝑑=−𝑉₁, (5) where 𝑉₁ is determined by 𝑉₁=−𝐸_𝐶𝑑=−𝑑Δ𝑞𝜀₀𝐴₁. (6)

According to (3) and (6), if the cross-section of the spark plug electrodes, 𝐴₁, is reduced without changing the electrodes distance, the ignition electrical field will be established faster.

2.3. Electric Field Built by Proposed Plug

Figure 5 shows the structure of the proposed spark plug, in which the cross-section of the spark plug electrodes, 𝐴₂, is reduced as a shape of sharp knife, and the positive electrode faces the negative electrode with their sharp end. With the same way, a Gaussian cylindrical shell is selected and an electrical field, 𝐸^′, is calculated as 𝐸^′=Δ𝑞𝜀₀𝐴₂. (7)

Figure 5 

The structure of the proposed spark plug.

From Faraday law, the relationship holds 𝐸⋅𝑑𝑠⃗=−𝑑Φ_𝐵𝑑𝑡=−𝑉. (8)

The ignition voltage that is established between the two electrodes is 𝐸^′⋅𝑑𝑠⃗=𝐸^′𝑑=−𝑉₂, (9) where the 𝑉₂ can be calculated by 𝑉₂=−𝐸^′𝑑=−𝑑Δ𝑞𝜀₀𝐴₂. (10)

2.4. Comparisons of the Electric Field and Ignition Voltage

The side views of the proposed plug and traditional plug are placed in line horizontally in order to distinguish the magnitude of key parameters. Figure 6 shows the side views. The electric fields in the spark plug of traditional plug and the proposed plug are in (3) and (7), respectively. If (7) is divided by (3), one can find 𝐸^′=𝐴₁𝐴₂𝐸_𝐶. (11)

Figure 6 

The side views of the proposed plug (a) and the traditional plug (b).

Since 𝐴₂<𝐴₁; then 𝐸^′>𝐸_𝐶. The 𝐸_𝐶 is estimated by 𝐸_𝐶=Δ𝑞𝜀₀𝐴₁=𝑖(𝑡)Δ𝑡𝜀₀𝐴₁=𝑖(𝑡)Δ𝑡^′𝜀₀𝐴₂. (12)

Thus, the following yields Δ𝑡^′<Δ𝑡. (13)

This derivation shows that the electrical field 𝐸^′ is established faster than 𝐸_𝐶 and the ignition charges are concentrated in a smaller cross-section. It results in an improvement of engine combustion efficiency. The voltages across the spark plug created by the proposed plug and traditional plug are shown in (6) and (10), respectively. As 𝐸^′>𝐸_𝐶, from (6) and (10), it can be obtained that 𝑉₂<𝑉₁. (14)

This reveals that the proposed plug can reduce the ignition voltage as well as EMI issue.

3. Experimental Results

To verify the functionality of the proposed spark plug, real-car test is carried out, and practical measurement is fulfilled. In order to complete the contrast test, key parameters of the proposed novel dual-electrode plug and the traditional one are listed in the following. A corresponding figure is also illustrated in Figure 7.(1)The radius of the positive electrode is 𝑟=1.2 mm.(2)The distance between positive electrodes is 𝑑=1.4mm.(3)The top cross section of positive electrode of the traditional plug 𝐴₁=3.77 mm².(4)The top cross section of positive electrode of the proposed plug 𝐴₂=2.40 mm².

Figure 7 

Expressing the key parameters of the proposed plug (a) and the traditional one (b).

In the test, a flyback-type capacitor discharging igniter is used as the plug driver. Figures 8, 9, and 10 show that the proposed plug has the feature of less time delay at the vehicle speed close to 1620 rpm, 2220 rpm, and 4500 rpm, respectively. Figures 11, 12, and 13 show the ignition voltages measured from traditional plug and the proposed plug. It can be found that the proposed plug needs much smaller ignition voltage than that of the traditional one at the speeds of 556, 838, and 1380 rpm, in turns.

(a)

(b)

Figure 8 

The waveforms of ignition timing under the speed of about 1620 rpm: (a) traditional plug and (b) the proposed plug.

(a)

(b)

Figure 9 

The waveforms of the ignition timing under the speed of about 2200 rpm: (a) traditional plug and (b) the proposed plug.

(a)

(b)

Figure 10 

The waveforms of the ignition timing under the speed of about 4500 rpm: (a) traditional plug and (b) the proposed plug.

(a)

(b)

Figure 11 

The waveforms of the ignition voltages under the speed of about 556 rpm: (a) traditional plug and (b) the proposed plug.

(a)

(b)

Figure 12 

The waveforms of the ignition voltages under the speed of about 838 rpm: (a) traditional plug and (b) the proposed plug.

(a)

(b)

Figure 13 

The waveforms of the ignition voltages under the speed of about 1380 rpm: (a) traditional plug and (b) the proposed plug.

4. Conclusion

In this paper, a novel dual-electrode spark plug for combustion engines is proposed, which can obtain an enhanced electric field to lower ignition voltage and EMI issue. As a result, fuel consumption and exhaust pollution can be readily alleviated. The electric field built in the proposed plug and the corresponding ignition voltage are discussed by Gauss law and Faraday law. To verify the excellent performance of the plug, real-car test is carried out. The proposed plug and a traditional plug are installed in an engine vehicle in turn. At a different speed, the measured results reveal that the proposed plug can lead to lower ignition voltage and have exact igniting timing.