Document:

March 5, 2014

 

Brean Capital LLC

1345 Avenue of the Americas, 29th Floor

New York, NY 10105

 

Ladies and Gentlemen:

 

As an inducement to
the Placement Agent to execute the Placement Agency Agreement (the “Placement Agency Agreement”), with respect
to a public offering of shares of common stock, par value $0.0001 par value per share (the “Securities”), of
ClearSign Combustion Corporation, and any successor (by merger or otherwise) thereto, (the “Company”), the undersigned
hereby agrees that during the period specified in the following paragraph (the “Lock-Up Period”), the undersigned
will not offer, sell, contract to sell, pledge or otherwise dispose of, directly or indirectly, any Securities or securities convertible
into or exchangeable or exercisable for any Securities, enter into a transaction which would have the same effect, or enter into
any swap, hedge or other arrangement that transfers, in whole or in part, any of the economic consequences of ownership of the
Securities, whether any such aforementioned transaction is to be settled by delivery of the Securities or such other securities,
in cash or otherwise, or publicly disclose the intention to make any such offer, sale, pledge or disposition, or to enter into
any such transaction, swap, hedge or other arrangement, without, in each case, the prior written consent of Brean Capital LLC (“Brean”).
In addition, the undersigned agrees that, without the prior written consent of Brean, it will not, during the Lock-Up Period, make
any demand for or exercise any right with respect to, the registration of any Securities or any security convertible into or exercisable
or exchangeable for the Securities.

 

The initial Lock-Up
Period will commence on the date of this Lock-Up Agreement and continue and include the date two months after the public offering
date set forth on the final prospectus used to sell the Securities (the “Public Offering Date”) pursuant to
the Placement Agency Agreement, to which you are or expect to become parties; provided, however, that if (1) during the last 17
days of the initial Lock-Up Period, the Company releases earnings results or material news or a material event relating to the
Company occurs or (2) prior to the expiration of the initial Lock-Up Period, the Company announces that it will release earnings
results during the 16-day period beginning on the last day of the initial Lock-Up Period, then in each case the Lock-Up Period
will be extended until the expiration of the 18-day period beginning on the date of release of the earnings results or the occurrence
of the material news or material event, as applicable, unless Brean waives, in writing, such extension. Notwithstanding the forgoing,
during the Lock-Up Period, the Company may close any offering or offerings of its securities (the “Subsequent Offering”)
at a price or prices that equal or exceed 115% of the price at which the Securities are sold provided that (1) any Subsequent Offering
will not exceed the aggregate purchase price of the Securities and (2) such Subsequent Offering will not occur until at least 30
days after the closing of the sale of the Securities.

 

    	 

    	 

    

 

The undersigned agrees
that, prior to engaging in any transaction or taking any other action that is subject to the terms of this Lock-Up Agreement during
the period from the date of this Lock-Up Agreement to and including the 34th day following the expiration of the initial Lock-Up
Period, it will give notice thereof to the Company and will not consummate such transaction or take any such action unless it has
received written confirmation from the Company that the Lock-Up Period (as may have been extended pursuant to the previous paragraph)
has expired.

 

The restrictions set
forth above shall not apply to:

 

(1)         if
the undersigned is a natural person, any transfers made by the undersigned (a) as a bona fide gift to any member of the immediate
family (as defined below) of the undersigned or to a trust the beneficiaries of which are exclusively the undersigned or members
of the undersigned’s immediate family, (b) by will or intestate succession upon the death of the undersigned or (c) as a
bona fide gift to a charity or educational institution;

 

(2)         if
the undersigned is a corporation, partnership, limited liability company or other business entity, any transfers to any shareholder,
partner or member of, or owner of a similar equity interest in, the undersigned, as the case may be;

 

(3)         the
exercise by the undersigned of any stock option(s) issued pursuant to the Company’s existing stock option plans, including
any exercise effected by the delivery of shares of Common Stock of the Company held by the undersigned; provided, that, the Common
Stock received upon such exercise shall remain subject to the restrictions provided for in this Lock Up Agreement;

 

(4)         the
exercise by the undersigned of any warrant(s) issued by the Company prior to the date of this Lock-Up Agreement, including any
exercise effected by the delivery of shares of Common Stock of the Company held by the undersigned; provided, that, the Common
Stock received upon such exercise shall remain subject to the restrictions provided for in this Lock-Up Agreement; and

 

provided, however, that (A) in the case
of any transfer described in clause (1) or (2) above, it shall be a condition to the transfer that the transferee executes and
delivers to Brean, acting on behalf of the Placement Agents, not later than one business day prior to such transfer, a written
agreement, in substantially the form of this Lock-Up Agreement (it being understood that any references to “immediate family”
in the agreement executed by such transferee shall expressly refer only to the immediate family of the undersigned and not to the
immediate family of the transferee); (B) in the case of clauses (1) and (2) above, such transfer shall not involve a disposition
for value; and (C) in the case of any transfer described above, no filing under Section 16(a) of the Exchange Act (other than a
filing on Form 5 made after the expiration of the Lock-Up Period) shall be required or shall be voluntarily made in connection
with such transfer or distribution.

 

    	 

    	 

    

 

Notwithstanding anything
herein to the contrary, the undersigned may enter into a written trading plan established pursuant to Rule 10b5-1 of the Exchange
Act during the Lock-Up Period, and the Company may announce the establishment of such a plan, provided that no direct or indirect
offers, pledges, sales, contracts to sell, sales of any option or contract to purchase, purchases of any option or contract to
sell, grants of any option, right or warrant to purchase, loans, or other transfers or disposals of any Securities or any securities
convertible into or exercisable or exchangeable for Securities may be effected pursuant to such plan during the Lock-Up Period.

 

In furtherance of the
foregoing, the Company and its transfer agent and registrar are hereby authorized to decline to make any transfer of shares of
Securities if such transfer would constitute a violation or breach of this Lock-Up Agreement.

 

If the undersigned
is an officer or director of the Company, the undersigned further agrees that the foregoing restrictions in this Lock-Up Agreement
shall be equally applicable to any issuer-directed Securities the undersigned may purchase in the above-referenced offering.

 

This Lock-Up Agreement
shall be binding on the undersigned and the successors, heirs, personal representatives and assigns of the undersigned. This Lock-Up
Agreement shall lapse and become null and void if the Public Offering Date shall not have occurred on or before March __, 2014.
This agreement shall be governed by, and construed in accordance with, the laws of the State of New York.

 

	 	Very truly yours,
	 	 
	 	By:	 
	 	 	Name:FIRST AMENDMENT TO LEASE

 

THIS FIRST AMENDMENT TO LEASE, dated as of the 17th day of December,
2013, is entered into by and between RREEF AMERICA REIT II CORP. MMMM7 WASHINGTON, a Maryland corporation ("Landlord"),
and CLEARSIGN COMBUSTION CORPORATION, a Washington corporation ("Tenant")-

 

RECITALS

 

A. Landlord and Tenant entered into that certain lease dated
August 19, 2011, as amended by that certain Commencement Date Memorandum dated November 1. 2011 (collectively, the "Lease"),

 

B. The Lease pertains to approximately 6,950 square feet of
space located in Building 1 of Gateway Corporate Center, having an address of 12870 Interurban Avenue South, Seattle, King County,
Washington (the "Existing Premises"), as more fully described in the Lease.

 

C. Landlord and 1'eiant desire to expand the area of the Premises,
change the Rent Schedule, and otherwise amend the Lease as more fully set forth below,

 

AMENDMENT

 

NOW, THEREFORE, in consideration of the mutual covenants and
conditions contained herein and other good and valuable consideration, the receipt and .sufficiency of which is hereby acknowledged,
the parties agree as follows;

 

1. Definitions. Unless otherwise specifically set forth
herein, all capitalized terms used shall have the meanings attributed to them in the Lease.

 

2. Notice Address is hereby changed to the following:

 

RREEF America REIT II Corp. MMMM7 Washington

c/o CB Richard Ellis | Asset Services

20415 - 72nd Avenue South. Suite 210

Kent. Washington 98032

 

3. Expansion of Premises. Commencing on February 1, 2014,
the Existing Premises shall be expanded by approximately 2,250 square feet (the "Expansion Space'), such that the Existing
Premises plus the Expansion Space shall thereafter be comprised of approximately 9,200 square feet (the "Premises") shown
on Exhibit A-1 attached hereto, which shall supersede Exhibit A attached to the Lease. Tenant accepts the Premises in its "as-is"
condition, without any obligation by Iandlord to make any improvements, repairs or modifications thereto.

 

4. Rent Schedule. The Rent Schedule for the period from
January 1, 2014 through February 28, 2017 shall be as follows:

 

    	 

    	 

    

 

 

5. Rent Adjustments; Tenant's Proportionate Share. Effective
as of February 1, 2014, Tenant's Proportionate Share of Expenses and Taxes shall be 2.12% of Gateway Corporate Center (having a
total NRA of 433.864 square feet).

 

6. Relocation of Premises; Tenant's Option for Early Termination
of Lease. Paragraph 4 of the Addendum to l -ease is hereby deleted in its entirety.

 

7. Effect of Amendment; Incorporation. Except as expressly
modified herein, all terms and conditions of the lease remain in full force and effect and are hereby ratified and confirmed.

 

IN WITNESS WHEREOF, Landlord and Tenant have executed this l-irsl
Amendment as of the day and year first written above.

 

	LANDLORD:	 	TENANT:
	 	 	 
	RREEF AMERICA REIT II CORP> MMMM7	 	CLEARSIGN COMBUSTION
	WASHINGTON, a Maryland corporation	 	CORPORATION, a Washington corporation
	 	 	 
	By:	/s/ Cathleen Meyer	 	By:	/s/ James N. Harmon
	 	 	 	 	 
	Cathleen Meyer, Vice President	 	James N. Harmon
	 	 	Chief Financial Officer
	 	 	 
	Date: 12/23/13	 	Date: 12/18/2013

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